Hi,
Apart from actually seeing the crystals on the logic board, I don't think so. If its all working okay, then I really wouldn't start poking around in there. Even if you found some, you're probably more likely to damage it cleaning it off than leaving it on there. Logic boards are pretty sensitive to static etc, so rubbing it with a cloth is probably not a good idea, and I certainly wouldn't use any cleaning agents on it.
As long as you're not noticing it impeding on your machine's functionality, I would just forget about it altogether. Logic boards are really pricey if you damage it.
Hope this helps,
Tom