Due to the 120kb rule signature's must be lowered in quality as most never come out in 120kb to go,
however many times i see really bad quality signature's in order to meet the kb requirement.
With Photoshop you can recreate your signature's in under 120kb without loosing the signature's quality and keeping the .png format
. Finish your signature and save it as .png format
. go to layer> new adjustment layers> posterize
. set the posterize somewhere between 20-40 levels [depending how big the file size is]
the higher the levels the less kb change it will make.
. after you picked a level [start with 30 and work your way up or down to make it 120kb or under] save it as a .png again and check what the kb size is now ,you can do this by going to your signature folder and clicking on the signature[the kb information should be posted on the bottom of the screen ,although im not sure if this is for all operating systems as i only run windows 7
. After the change meet's your requirements , upload and use!
This is a very easy process and barely changes the quality of the signatures.
Hope this small tutorial help's some people out,and feel free to ask any questions!