http://www.ebay.co.uk/itm/Omega-Tis...470291268?pt=Wristwatches&hash=item2308ba6f44Purchases made through these links may earn this site a commission from the eBay Partner Network I've never seen a dial signed both Omega and Tissot before, the patina leads me to think it's original. Matt
Both are sister companies and there are dials which are double signed if I am not wrong. Think there was a thread somewhere here discussing this. The dial looks original to me.
These dials marked both tissot and omega were done in late 1930s watches - typically in chronographs and marine watches though I have seen them in other styles as well. For the collector, these are valued as tissot watches rather than omega.