Sorry, I don't know your answer in Spanish, but I think what you're looking for is called a stock (exchange) symbol or a ticker symbol in English.

símbolo de ticker is the term used on Yahoo Finance

símbolo de ticker is the term used on Yahoo Finance

My guess as Spanish learner would be código de inventario but PLEASE, native speakers, tell us if that is correct! That should at least give the hispanohablantes a clue because what Logan said about stock code sounding like something to do with the stock market is the same thing I thought. Stock as in inventario, las reservas, existencias etc. And code as in código o numeros.