ISIN numbers are commonly used in the European markets instead of the Symbol / Market system that AST uses. Internally AST fetches its quotes from the US Yahoo! Finance. This version of Yahoo finance does not support ISINs at all. However a European version does support ISINs, and it also translates them into symbol / market format. For example:
That is, symbol is MLACO on Euronext Paris. One issue I see here is we have no way to lookup an ISIN, only to convert one into the system AST uses. However this is better than nothing. I will look into getting a database of ISIN numbers.
Another issue I see is what to do if the market does not exist? One furthur issue, if ISIN numbers are going to be stored by AST is that the length of the symbol field must be increased (its only 10 characters now which is enough to accomadate 9 letter CUSIPs).