Can I setup a different signature for each of my Gmail aliases

Yes – you can do that. Here is how to design email signature for of your Gmail aliases is explained in the support note.

Can have multiple signaures for the same Gmail email address?

Yes – that is possible. You just need to create a “plus” or “dot” Gmail aliases as described here (i.e., create for tips, etc.). Then you just need to design a signature for each of your aliases as described in this support note.