For some, the income we receive from these campaigns is a big portion (0.3BTC isn't exactly a small amount). I am waiting until I get paid then will decide the best course of action.
Its an interesting dilemma.
If people are going to neg rep you then should do that for all those who are sporting the cryptcominer or gawminer signatures. I suggest you add a banner to your posts disclaiming the signature or directing people to the relevant thread.
If its proven to some reasonable degree that they scammed (I am sure they did), then the escrow holders should take the call and divide up the money, or settle it with some lower pay.
The issue is that these two sites have not scammed
yet. While I am confident that both of these sites will scam, IMHO I think pre-emptive actions are unfair.
Regarding the signature ads: The exchange is for displaying an ad. The exchange does not involve you astrosurfing or defending them. Why not continue to carry the signature, but add a visible disclaimer? You have a free line.