And how do you tell if it is real or a fake? I tried the Omega database but cannot find this model - other 2256 / 1 look very different.
The 6M serial number dates it to somewhere between 1923 and 1933. As it is a low 6m number, it's probably early/ mid 1920's. The movement appears original and most likely to be a cal 12''' S 7-16 p, which was one of the earliest Omega wristwatch movements. The case is possibly either silver or white gold, as this is the period when stainless steel first started to be used for wristwatches. The closer it is to the late 1920s/early 1930s the more likely it is that the case is steel. The design of the dial is correct for the period, although it looks like it was repainted at some point - probably a long time ago.
Funny you say that as the 12''' movement was used in ladies pendant watches. And from 1900 in the first Omega wristwatches. But it's too small to be a men's pocket watch movement (26.5mm). But having done a bit more research I think your movement is more likely to be a wristwatch designed movement derived from the 12'''. Namely a cal 23.7. The pictures below show what I mean. The cal 23.7 pictured also happens to have a serial no close to yours. You'll probably be able to tell for sure by measuring the movement. The first one is 26.5mm and the second one is 23.7mm.
Hi, IMHO, based on the serial number and on the click of the mainspring (don't know the English translation) it's a 23.7. 23.7 was used in men's caliber at that time. Caliber and case are both genuine Omega, but Omega didn't put case ref in the mid 1920's, they started after WWII (can't remember the exact date right now), so for me it looks like a recasing of a mid-20's 23.7 in a much later case. Is there a spacer ring in the case, the inner part looks of a different color.