As signature campaign managers don't have access to IP, it is easy to join from multiple accounts. If you post in same style, they might catch you.
-MZ
slush.
I see no real problem when I person tries to join signature campaign with 2 accounts. As long as your posts are legit, coherent and are not spammy slush it should be ok. Some companies do not forbid it at all.
It might not be a problem, especially if they're making decent quality posts, but campaign managers are free to state their own rules though they're only enforceable by them and like others have mentioned very hard to police effectively (though stingle seems to do a good job but that usually down to people being sloppy with their addresses.