Maybe. But don't forget that signature space is limited. Chances are that most of that character space is already lost because of the sig you are wearing, so you won't be able to do much with what remains. One way around it is if a Hero/Legendary would wear a sig for a Member/Full Member, which leaves him with enough room to include other things in his signature space.

Good campaign managers surely check if there are additional lines and entries in the signature that shouldn't be there. It's against the rules to have that.
Here is just one example: