Since forums are basically more concerned with fighting spammers than scammers, it would make more sense to just flag fraudulent participants from the signature bounty. I often see them littering the forum environment with one-line replies in some of their favorite sections (altcoins), if I'm right it's because they have to meet the post quota of all their accounts.
Forum is concern in dealing with sharing ideas and topic regarding bitcoin and its external and internal processes and uses. I dont think these are priority of forum to clean up such thing regarding bounty.
Some one liner post arent considered spam especially if they have sense. Why would you make a long response right if the answer needs a short one. There is an exception to that. Quota on signature can be counted for constructive one. A short post doesnt mean its not valid at least some manager consider it as long as it on point.