That's pretty big for a sig pic. I highly recomend that you decrease at least one of the dimentions by 1/3.

As for text, that's a pretty easy thing to do. You just choose your text tool, choose the place to add text, type your text, and change it's size and font.

If you want something fancier, try some effects on the text till you find one you like.
--WetWired