well, signatures are really basic graphics... even the best ones. if you're dedicated enough, you can learn how to make awesome signatures in no time... just look up some tutorials, learn your program, etc... then once you're good enough that you can run on your own fuel start switching/mixing it up, adding your own "niche" (per se) to the works, stuff like that.
just like becoming great at drawing or singing, working with computer graphics (and actually making good work) is something that takes time and dedication. keep in mind if you're pursuing a career in graphics, learning signatures is a really good entry point for that field.