To me, it's all in the font itself! Sometimes you just have to download a bunch of ones you like on a great website.
DaFont.com is the best, if you ask me.
A lot of times I will write the text out, and then highlight it and just arrow down through everything and stop on the one that I think fits the "style of the signature." Some of the best blending options (if you are using Photohop) is a gradient that fades from light to dark with matching colors that are in the signature. Sometimes just plain letters with a slight drop shadow on them, or even a thin stroke around the edges....
Every font is different, and not everything works every time. It's a lot of playing around!