More than likely this is a custom case. To determine what you have with any degree of certainty you would need to provide picture of the movement and the inside of the case back.
It looks to be a 1920's watch, judging by the fixed loop bars. There were a few variants on these decorated cases around so it may be too early to conclude it is not an Omega case. The dial looks original in good condition, although the photo's are a bit blurry. There isn't a lot of value in these, unless the case is gold. Did you buy it or "find" it ?
My nan was having a clear out and she was about to throw it so i took. All i knew about it was that it came from Spain pre civil war
It's not a custom case, but an Omega factory one. Shouls have a 26.5 SOB Inside. I have one with an Omega signed nickel case, I don't know the reference (could not find it in any catalog or advertising) and don't know if it was also produced in gold or gold plated case. I think the dial was repainted on your Watch. Here is mine : I created a thread here about this Watch : http://omegaforums.net/threads/does-anyone-know-something-about-this-unusual-26-5-sob.8511/.