i'd actually suggest calling about this rather than leaving it alone... don't call up and ask anything stupid, but i think it's entirely reasonable for you to call and inquire about the status of your pending (or potential) charge. if they don't find out what it is, you could be facing paraphernelia charge; if they do, possession of a controlled substance would be my guess.
on the flipside, i guess there's something to be said for leaving it alone and hoping they just forget about it or get lazy or something, which is entirely possible, but at some point i would want to know what/if they were charging me w/