I think it is okay to participate multiple bounties. Signature campaigns on the other hand is different you can only wear one signature at a time. And you can't join the same signature campaign with your alt account. It is cheating and you will be banned for it
Well...
A signature campaign is a deal between you (the campaign participant) and the company you're promoting (usually represented by the campaign manager). There are some forum rules on how to behave in a civil way, but there aren't any rules that govern things like whether or not alt accounts are permitted or whether or not you can join 2 campaigns at the same time.
This means those rules are basically between the participant and the company... The company proposes a set of rules, and participants usually agree to the rules set by the company in order to be able to work for them.
It's perfectly possible (eventough i've never seen this) that a company allows an advertisement for a different company next to their advertisement in your signature area (eventough this will mess up the advertisement's design).
It's perfectly possible (eventough it's rare) that a company doesn't care if you join with alt accounts...
The bottom line is: there are forum rules you cannot break unless you want to get banned, and there are rules set by company's that run signature or bounty campaigns... As long as the signature/bounty rules don't contradict forum rules, everything should be ok
