You can do that already, just cut down the amount of characters allowed in a signature so they attract less attention.
Bad idea IMHO. Signatures are used for personal advertising too without much designs.
But wouldn't that result in a dramatic reduction of the payout? Because the campaign company would be getting less views.
Only if they don't check and ban people from their campaign correctly.
-MZ
If 50% of users turn off signature viewing, then the signature campaign is getting 50% less exposure. So won't they want to pay less?