Here are a few alphabet charts you can use to sign your work. The heights assume you are using mixed upper and lower case; less space is required for all upper or all lower case.
I love cross stitching and this is a fantastic site!! I am ready to pick my next piece and I look forward to picking one from your site - I am very impressed. Particularly with the option of having the pattern printed in larger text, that will save me the trouble at the photocopier!