I, on the other hand, would like to see a rule that one can participate in signature/bounty campaigns exclusively with one account in one campaign,
This rule is already in there for most of the campaigns.
Just like scams aren't moderated by the admins/mods, such things arent too. Thats why you got "campaign managers" for this job and most of them do well imo..
I think it would be fair to all other users of the forum who have only one account and may not be able to get a place in a sig campaign because someone uses their alt accounts in 4 or 5 different sig campaigns.
If someone got 4-5 or more accounts just for the sake of participating in sig. campaigns, chances are they wont get accepted in any, since such users are mostly broken (i)nglish sh*tposters. Again, a good manager can easily spot them.
Also, I believe most newbies who need technical help, forget about their account after their problem is solved and come back later again with new account with a new problem. Thats why you see many 1 post brand new accounts in the forum. Most are alt accounts of each other. If theymos starts IP banning ppl, they wont be able to comeback again for help lol.