Every transaction line on a Form 4 carries a single letter code. The code is the fastest way to tell a genuine market trade from a compensation event, and misreading it is the most common error new readers make. A large share movement with the wrong code can look like a bold purchase when nothing of the kind happened.
Code P is an open market or private purchase of a non-derivative security. The insider chose to buy, paid the stated price, and used personal funds. Code S is the mirror image: an open market or private sale. These are the only two codes that represent voluntary trading at market prices, which is why this site shows only P and S transactions in its main feed. Filtering the feed this way keeps grants, exercises, and tax events from crowding out the trades that reflect an actual decision to buy or sell.
Code A is a grant, award, or other acquisition under a company benefit plan. Shares arrive as pay, often with vesting conditions described in the footnotes. No money changes hands at a market price, so an A transaction says little about what the insider thinks the stock is worth today. Code M is the exercise or conversion of a derivative security, typically an employee stock option being exercised into shares. An M transaction can look like a large acquisition in Table I, but the decision behind it is often driven by an approaching expiration date rather than a fresh view on the stock, and it is frequently paired with a sale or a tax withholding entry.
Code F covers shares delivered back to the company, or value withheld, to pay an option exercise price or a tax liability when restricted stock vests. It is bookkeeping that follows compensation events and is not a decision to sell in the market. Code G is a bona fide gift, in or out. A gift moves shares without a price and reflects estate or charitable planning more than market judgment. Code C is the conversion of a derivative security, such as convertible notes or preferred stock turning into common shares under preset terms. The conversion ratio was fixed when the instrument was issued, so a C code records mechanics, not a new purchase.
Several less common codes complete the list. J covers other acquisitions or dispositions described in a footnote, a catch all used for transactions that fit nowhere else, such as distributions from a plan or a change in the form of ownership. K reports transactions in equity swaps and similar instruments. U covers shares tendered in a change of control transaction. V marks a transaction that was reported voluntarily earlier than required. W covers acquisitions or dispositions by will or inheritance, and X and Z relate to older option exercise reporting and deposits into or withdrawals from voting trusts. In daily practice, P, S, A, M, and F account for the overwhelming majority of lines a reader will see.
Read the code before the share count. A 50,000 share A is routine pay; a 50,000 share P is a major purchase. Also read codes in sequence across both tables, because real events often span several lines: an M in Table II, an acquisition in Table I, and an F or S beside it to cover taxes or to sell the exercised shares.
Codes explain the type of a transaction, not whether it was a good decision. This guide is educational and is not investment advice.