Gorgeous Omega!
It's not totally uncommon for some very vintage original dials to not have "Swiss Made" or "Swiss" markings. Sometimes I chalk it up to redials but the ones I've seen without "Swiss" or "Swiss Made" are usually from the 30's to 40's. Might have something to do with who cased them as well as some swiss brands back then often had the watches cased by a third-party in Canada or the US to get around tariffs.
This is my late 30's/early 40's Lemania (which was acquired by Omega around this period) with an original and untouched enamel dial w/out any swiss markings
