As far as other things mentioned to get in the top list, why wouldn't you want to help a company by giving an occasional post in their thread or mention them in other threads?
Because that's not what you're getting paid for when you join a sig campaign. It's a simple financial transaction: signature/avatar rental for a certain amount of bitcoin, and the campaign member may or may not even personally like (or even know much about) the service they're promoting.
This just kinda/sorta sounds like you want thread bumping (which is against the rules) but don't want to come out and say it. I'd probably eliminate that from any helpful/not helpful criteria, but that's just me.