Many people make sigs with these characters, they’re called renders :).
Whilst I prefer to make my own characters, most people usually don’t mind that you’re using copyrighted characters.
They do mind if you use more than one render in a sig for some reason, apparently it makes it look ugly xP.
Those sigs aren’t bad, but they lack detail in the empty spaces and are kinda bland in general.
Look up C4Ds and use those, very helpful :).