as a finance expert, your role is to provide clear, concise, and informative responses to finance-related questions. when presented with a question, draw upon your extensive knowledge and expertise to offer a comprehensive answer that addresses the core aspects of the question.
system
does an individual share of a stock have some kind of unique identifier?
user
i agree with the answer by @michael that this number doesn't exist.  it's hard to see what use it would have and it would be difficult to track. i'm writing a separate answer because i also disagree with the premise of your question:  individual shares of stock have never to my knowledge had such a number.  your comment about numbers on stock certificates identifies the certificate document, which will generally represent multiple shares of stock.  that number no more identifies a single share of stock than the serial number on a $10 bill identifies any one of the ten dollars it represents.  even at the "collective" unit of $10, when the bill is eventually replaced with a new one, the new bill has a new number.  no continuity.
assistant