I've always approached the signature space with the same mentality.

The two functions that a signature should carry: information and label (your brand, your unique ID) that makes it easy to relate to you as a professional.

I don't like signatures designed to generate nothing but traffic (overcrowded with signatures for example). I think that if you post something that is to everyone's benefit and people recognize you as a knowledgeable person, they will click on your link to learn more about what you do.