Market maker signals are a fixture of penny stock and OTC trading folklore. The theory is straightforward: market makers, unable to communicate directly without running afoul of SEC rules, use coded trade sizes to pass intentions to one another. A 100-share print means one thing. A 300-share print means another. A 500 signals something else entirely.
That is the theory. The evidence for it is thin.
Understanding what is actually real here, and what is noise, matters more than memorizing a list of signal codes. This article covers what market makers do, what the signal theory claims, why it is disputed, and what traders can actually observe in Level 2 and Time and Sales data that is worth paying attention to.
What Is a Market Maker?
A market maker is a firm or institutional entity that provides liquidity by continuously quoting both a bid and an ask price for a given stock. When a retail trader places a market order to buy, the market maker is often the counterparty filling that order. When there is no natural seller available at the current price, the market maker steps in.
Market makers profit from the spread. Buy at the bid, sell at the ask, repeat thousands of times per day across many stocks. In liquid, large-cap names the spread is a penny or less and turnover is rapid. In thinly traded OTC and penny stocks, spreads widen considerably, which is precisely where market maker activity becomes more visible and more impactful.
On Nasdaq-listed stocks, market makers are identified by 4-letter market participant identifiers, or MPIDs. These IDs appear on Level 2 screens next to each quote, letting traders see which firms are posting bids and asks and in what size. This is the window through which the signal theory is supposed to work.
The Signal Theory: What Traders Believe
The premise is that direct communication between market makers about pending orders constitutes illegal coordination. To work around this, so the theory goes, market makers execute small trades in specific share quantities to signal intentions to other market makers observing the tape.
The most commonly cited signal list includes:
- 100 shares: I need shares (buy signal)
- 200 shares: I need shares but do not take the stock down
- 300 shares: Take the stock down to accumulate shares
- 400 shares: Keep the stock trading sideways
- 500 shares: Gap the stock up or down
- 700 shares: Move the price up
- 800 shares: Prepare for increased volume
- 900 shares: Let the stock trade freely
- 911 shares: News or press release incoming
- 1000 shares: Suppress the move
- 2100 shares: Let it run
The argument for why these would be detectable: the commissions on trades of this small size would exceed the value of the shares in many OTC penny stocks. A trader paying $5 in commissions to buy $2 worth of shares makes no economic sense. The only rational explanation, believers argue, is that the order is a message, not a trade.
Why This Theory Is Disputed
The SEC prohibits collusion and coordinated signaling between market makers. If the signal system described above were real and systematic, it would constitute market manipulation. There have been no enforcement actions, whistleblower cases, or prosecutorial findings establishing that this coded numbering system exists as an industry-wide practice.
The signal theory also has a basic structural problem: modern electronic markets move far faster than any signal-reading system designed for human eyes could practically operate. A market maker intending to communicate via tape prints would be relying on another market maker to (1) notice the specific print, (2) identify it as a signal rather than a normal odd-lot trade, and (3) react accordingly, all within a market environment where algorithmic execution operates in milliseconds. The theoretical mechanism is not well suited to the actual speed of contemporary market structure.
The signal codes have also proliferated through retail trading communities in ways that make them less useful as private communication, even theoretically. If the codes are publicly listed on penny stock forums and trading education blogs, they are no longer a private language.
None of this means market makers do not influence prices. They do. The distinction is between a secret coded communication system, which lacks credible evidence, and the real mechanics of how market makers operate, which are observable and worth understanding.
What Market Makers Actually Do to Prices
The observable effects of market maker behavior in thinly traded stocks are real, even if the signal codes are not. Traders watching Level 2 and Time and Sales on low-float OTC stocks will see all of the following at various points.
Controlling a Price Level
When a single market maker is filling a large institutional order, they often appear repeatedly on both the bid and ask side of a stock, keeping the price range tight while they work the order. A stock that should be moving based on volume and news activity stays pinned. This is not mysterious, it is an artifact of a single participant controlling order flow while executing a large position. When the order fills, the constraint disappears and price moves quickly to a new level.
Traders who watch Level 2 and notice one MPID dominating both sides of the book for an extended period are seeing the real version of what the signal theory gestures toward.
Iceberg Orders
An iceberg order is a large order that reveals only a fraction of its total size to the market. A market maker with 100,000 shares to sell might display 1,000 shares at the ask repeatedly. Each time those 1,000 shares trade, another 1,000 appears. The effect on Time and Sales is a series of prints at the same price level, often at the same size, creating a wall of resistance that keeps the stock from breaking through.
Iceberg orders are a legitimate institutional execution technique, not manipulation. But recognizing the pattern on the tape matters. When a stock keeps hitting the same price and repeatedly failing to break through, with consistent print sizes at that level, an iceberg is a plausible explanation. Once the order fully fills, the level clears.
Spoofing
Spoofing is placing a large order on the bid or ask with no intention of executing it, then canceling once it has had its desired effect on price. The large bid creates the impression of buying support. Other participants see depth at that level and buy above it. The spoofer cancels the bid, the artificial support disappears, and the price drops.
This is illegal. The SEC and CFTC have brought numerous spoofing enforcement actions, and it remains a live concern in low-liquidity markets. On Level 2, spoofing appears as large orders that materialize and disappear quickly, particularly near key support or resistance levels. The tell is speed: a genuine large order absorbs prints against it. A spoof order cancels before it trades.
Printing Outside the Market
In very thinly traded stocks, market makers will occasionally print trades at prices above the current ask or below the current bid. These anomalous prints show up on Time and Sales. The purpose is typically to mark a stock at a specific price for settlement or reporting reasons. These prints are not entry or exit signals. They are a data artifact of market structure in illiquid names.
Level 2 and Time and Sales: What to Actually Watch
For traders working with penny stocks or low-float OTC names, Level 2 and Time and Sales are the primary tools for reading market maker behavior. Not because signal codes are real, but because market depth and order flow reveal what large participants are actually doing in real time.
On Level 2
Watch for concentration on one side of the book by a single MPID. If one market maker holds the ask at a specific price with consistent size, they are likely managing a large sell order. When that MPID steps away, the level clears.
Watch for the ask collapsing. When multiple market makers pull their offers simultaneously, it often precedes a sharp upward move because there are no sellers willing to hold at current prices.
Watch for the bid stacking. A sudden deepening of bids below the current price can signal institutional interest supporting the stock. It can also be a spoof. The question to ask is whether those bids are absorbing trades or disappearing when price approaches them.
On Time and Sales
Consistent print sizes at the same price level suggest an iceberg. The stock is not breaking through because there is a systematic seller at that level, not because the level is technically significant.
Large green prints at the ask, in rapid succession, indicate buying pressure. Large red prints at the bid indicate selling pressure. When green prints are growing in size through a move, momentum is real. When the prints start shrinking even as price continues higher, the move may be losing conviction.
Pay attention to the speed of prints. A stock printing 20 times per second is in very different condition than one printing twice per minute. Speed reflects urgency. A sudden acceleration in print speed, particularly on green prints above a breakout level, is more useful information than any three-digit share count theory.
The Honest Assessment
The coded signal theory persists because active traders in penny stocks are looking for any edge in a market where information is scarce and institutional behavior is opaque. The intuition behind it is not entirely wrong: unusual trade sizes in low-value stocks do sometimes reflect institutional mechanics rather than organic retail activity. But the specific numbering system is not backed by evidence and should not drive trading decisions.
What is worth taking seriously is the underlying principle: market makers leave footprints. How they manage the bid and ask, how quickly they absorb orders, whether one participant is dominating the book, whether large orders appear and disappear, all of this is visible in Level 2 and Time and Sales to a trader paying attention. That is the legitimate insight buried under the folklore.
Trade the observable mechanics. The coded signals are a distraction.