I normally use the IPDB pics as a fairly good guide for this sort of stuff.  Sure enough, the only pic of a coin door doesn't have a decal on it.  Have you got or maybe search for a Fathom flyer to see what is on the flyer.

Yep, that's what I found too. Thanks for checking anyway.

On the back page of the flyer ;

http://www.pinballrescue.net/Decals_Coin_Door.html

"Part I.D. BLY-CD1" - It is the standard decal that was on all the early Ballys.

Thanks Nino, I have a spare one of these so I was hoping it was that one.