Even if you asked and were refused (unlikely in such a low-profile venue as a coffeehouse), anyone interested in your music is sure to seek you out after the slot and ask. Also, if the MC doesn't announce YOU as a player who's been featured at this venue before (which implies that you're a regular and at least half-way decent, thus might well have made recordings), they're not really doing their job to its fullest extent. Hardly any audience members are not going to know that most good musicians have recorded themselves to a technically high level, so while you might lose a few such ignoramuses, that's hardly worth losing sleep over.