Norway 1 Krone 1879

Here's a 1 krone of Norway dated 1879 with a difference.

There's a incuse omega symbol to the left of the king's neck on the obverse.







I asked the coin museum in Oslo, and their reply was
"We don't have any coins from Oscar II with such an initial and as far as I can see there's no catalogues mentioning it either. It's kind of difficult to say from the photo, but are you certain it's not a secondary mark?

The swedish coins of Oscar II has got initials at the same place, but thats L.A. (Lea Ahlborn, the engraver) and these are not on the Norwegian coins."

I find their answer rather strange because I can't see initials in the same place on any of my Swedish coins of Oscar II.

Have you come across this mark on coins before, please ?