Here is really a simple hack,which I want to share with everyone.This method however works only with Firefox.
STEPS:
1.Download the Firefox extension: Blank Canvas.
2.Install the plugin.

3.Now if you sign in to your GMail,you can automatically see a signature drop down menu.(Works only in Firefox!)



6.Finally,one can see the signature added automatically to your email signature.You can even customize your signature according to your friends,business etc.

Try this simple hack!