Go to a DIY market or a model kit store and yourself some epoxy or nitro-based putty.
I can highly recommend Tamiya 2 component epoxy putty for bowling ball repairs, e. g. when you have shallow notches in the surface. You get it in good plastic model kit shops and it comes in various versions with different "open" times. Just take 2 bist of the stuff, weld it together for some time and fill scratches or the serial number engravings with a flat spatula. The material does not shrink and has over night the hardness of coverstock resin, can be sanded or polished with no prblem, and adheres very well to the rest of the ball. Nitro-based putties are cheaper, but more brittle and might come off through vibrations etc.
Only downside of the Tamiya putty is its color - light ochre or green, depending on the version, you cannot add other colors.
Here's a pic of the ochre standard stuff on my Blade Particle:
http://www.putfile.com/pic.php?img=4196518Will work perfectly to fill any engravings
Here a link to the stuff's packaging (green, longer open version):
http://www.hobbylinc.com/htm/tam/tam87052.htm--------------------
DizzyFugu - Reporting from Germany
Confused by bowling?
Check out BR.com's vault of wisdom: the unofficial FAQ section