Well known fake from about 1950s/1960s.
Yours has wrong size second/minute and hour hands for that dial, not that it's a big deal.
The thing is, these watches usually had a decent Swiss movement like an AS1130 or similar so they were a reasonable watch to begin with, but unscrupulous people realised it had more value with "Omega" on the dial rather than "Acme" or "Timex".
As a fake it's hardly worth getting serviced/repaired but it's a nice memento of your grandfather who probably had a bit of a chuckle every time he looked at it.
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