It's a genuine Omega that has been used ( & abused )
Omega referred to this range as the Calyspo seamasters & this is a MK III.
Case Ref 396.0975
Made around 1985, It should have a 1432 quartz movement in it.
I'm a little bit surprised because I have only ever seen the black dial, with red markers, in a black PVD case. Usually the stainless case had either a white or silver dial in it.
The minute hand has been repainted, it should be dayglo Orange ( like the PloProf hand ) & the lume is missing from the centre of the hand.
I can't see the Omega symbol on the crown, it could be a replacement.
Here's a link to the same watch ( I believe ) that was recently in eBay. The seller stopped the auction early.
Crappy Seamaster 120 in eBay
I see someone bid $227 for it. IMHO it wasn't even worth the opening price.
If you're interested in one of these,keep your eyes open. they popup now & then...
'POP'
Ooops there's another now in the Bay ! => Another 120 Calypso quartz
But again this one is in terrible condition. ( redial & paint removed from the bezel )
This is a MK I ( the bracelet attaches differently ) & has a 1337 movement.
I hope this helps.
Steve