Stock Spam: Sell Signal?

I take it as a given that every stock touted via spam is, in fact, the subject of some sort of pump-and-dump scheme. That is, someone currently owning significant amounts of the stock (or options) is praising it, with the intent of causing upward motion, at which time they will sell their shares. So stock spam should be a reliable leading indicator of a loss of value. Therefore... Oh, you can't sell penny stocks short.

Never mind.