I use the same black font and size, get some lyrics that I like, and find a picture. I use the colours in the picture, and tinker around with bolding, and italics and such.
I prefer ones that match with colours, in particular. Or maybe even what it says.
The one I have now, Spencer's making a heart with his fingers, and the signature is a Homesick At Spacecamp reference. "My smiles are an open wound without you, and my hands are tied to pages inked to bring you back." The colours match [black&white picture scheme], but as far as if the lyrics and avatar itself match, no. xD
I'm about to change my avatar/signature, though. The one coming up's going to be [x] this. The signature's gonna be, "Maybe it's not my weekend, but it's gonna be my year, and I've been going crazy, I'm just stuck in here." The boy looks like he's stuck in a box or whatever, so the lyrics and the signature would relate that way, and I'm obviously going to make the colour scheme the same. xD