Help Seamaster Deville Pro’s: What is this

I have an Omega Seamaster Deville with S1052057 on the side of the watch behind the dial you turn to move the hands. I couldn’t find any engravings until I pulled out a lighted magnifying glass. I think these are the letters/numbers I see. I can’t find anything like it online or on eBay or anywhere. It has 3 small diamonds at the 6, 9 & 12. The band has been replaced but the watch itself is original from my husband’s grandfather. My husband is 56, his father is in his 80’s, so his deceased grandfather owned the watch.