I kinda like skulls. Probably not for the same reason other people like them, but...
I counted them up on my Metallica Pro and there are 14 total in the original artwork. There were two in the back corners on the plastics that I missed at first, but my son pointed them out to me. (I have the coffin skull mod that adds 3 but not counting those.)
Also, I have only 1 on my Buck Rogers, but it's a really cool skull with crazy horns.
Post if you have a machine with skulls in the original artwork, and tell me how many you found.