Multiple Signature Campaigns At The Same Time...

[Cast12]

There's no way to get multiple signature campaigns at the same time do to the rules the signature campaigns have set forth. Even if there was, you'd most likely run out of space to put on your signature.

[Arcteryx]

I have seen some individuals wearing another personal message from another campaign that is not the same as their signature. Even if the signature does have an avatar included in it's campaign I would think most campaigns would not allow this in the slightest. It is cross promotion after all.