Omega includes a logo on the inside center of their round acrylic (hesalite) crystals, today most often noticed on Speedmaster Professionals.
Omega began using hesalite in the 1940s, perhaps before. When did they begin marking the crystals with the interior Omega?
Did Omega put the interior logo on certain models or all models?
Was the interior logo ever placed on other than round crystals (because I don't recall seeing it on squares or rectangles)?
I cross posted on vintage and Omega forums as well. I'm really hoping to find an answer!