Hallmark guessing C Shape Conny

Hey everyone,

I came across an Constellation C Shape model with an "OM" dial. The pictures of the seller a pretty bad. Actually catastrophic.

There are no hallmarks on the lugs just this weird looking and hard to recognise something between the lugs. Unfortunately he isn't able to open the caseback...

Has anyone ever seen hallmarks on C Shape Constellations between the lugs and can help me figuring out wether it is solid gold or not?

My first impulse tells me that it should be solid gold (also in combination with the ‘OM’ dial) but I would prefer to get a few more opinions, even if it can only be clarified beyond doubt by opening the caseback.

thanks a lot and all the best
David