Form 4 Transaction Codes: What P, S, A, M, and F Mean

• →P: open-market or private purchase. The one that matters.
• →S: open-market or private sale.
• →A: grant, award, or other acquisition from the company (stock compensation).
• →M: exercise or conversion of a derivative, usually stock options.
• →F: payment of exercise price or tax by delivering shares to the company.
• →G: bona fide gift.
• →D: disposition to the company, for example in a buyback or a forfeiture.
• →C: conversion of a derivative security.

A common pattern is an option exercise (M) and an immediate sale (S) of the same shares. The insider is cashing compensation, not expressing a view. Headlines that count this as "insider selling" overstate it. A pure P line, with no matching award, is the opposite: the insider chose to own more.

The alert pipeline keeps code P buys of $50,000 or more that are not part of a 10b5-1 plan, and logs significant non-plan sales only to detect clusters. Grants, exercises, and tax withholding never produce an alert.

The SEC publishes the complete table in the Form 4 instructions. Beyond the common ones above, these appear often enough to recognise:

• →J: other acquisition or disposition, explained in a footnote. Read the footnote; J covers everything from a stock split to a transfer into a trust.
• →K: a transaction in an equity swap or similar instrument.
• →L: a small acquisition under Rule 16a-6, exempt from the usual reporting timing.
• →W: acquisition or disposition by will or the laws of descent and distribution.
• →Z: deposit into, or withdrawal from, a voting trust.
• →U: shares tendered in a change-of-control transaction, for example into a takeover offer.
• →I: a discretionary transaction inside an employee benefit plan, such as moving money in or out of a company-stock fund in a 401(k).
• →X: exercise of an in-the-money or at-the-money derivative security.
• →H: expiration of a long derivative position. E: expiration of a short derivative position. O: exercise of an out-of-the-money derivative.

Table II, the derivatives table, uses the same codes. An RSU vesting shows as an M in Table II (the unit is converted) paired with an A or M in Table I (the shares arrive), and often an F on the same day for the shares withheld to pay tax.

The code and the price column confirm each other. A code P row should show a price close to where the stock traded that day. A code A row shows $0 or a nominal figure, because the company issued the shares. A code M row shows the option's exercise price, which can be far below the market and says nothing about what the insider thinks the stock is worth now. A code F row shows the market price on the day the shares were withheld, but the insider did not decide to sell anything.

Two reads that catch people out: a code P at a price well below the market on a day when several insiders report the same price is usually a private placement or a registered direct offering, not open-market buying; and a code S under a 10b5-1 plan, marked by the checkbox or a footnote, was scheduled months earlier and carries little information about today.

Suppose a CFO's Form 4 shows three rows dated the same day: M, 20,000 shares, price $12.00; S, 20,000 shares, price $41.50; F, 4,100 shares, price $41.50. The insider exercised options at $12, sold the resulting shares at $41.50, and delivered 4,100 shares to cover the tax bill. The "amount owned following" column will be almost unchanged. This is compensation being converted into cash. It is not a bearish call on the company, and an alert service that counts it as a $830,000 insider sale is counting noise.

Now suppose a director's Form 4 shows one row: P, 25,000 shares, price $41.20, no plan checkbox, footnote "open market purchase". The director paid about $1.03 million of their own money at the market price. That is the row an insider-buying alert exists for.