Another tell tale sign is to turn the machine on, look at the boot screen, decypher the displayed serial number (sn) and check it against the sn on the cabinet.  Since all WPC-s & WPC-95 use the secure pic chip which contains the actual sn of the game it is harder to fake this.  Of course an original machine is more than likely to have the correct pic chip for the original title too, this of course can be circumvented but the sn and game number will not match.  MM is game number 559 as displayed.

Cheers