Antique French Pocketwatch Marked SG with a Key in Between

by Nessa
(USA)

Hello, I have an antique 18K gold enamel pocket watch. The goldmark is a horses head (stamped in two places) which I understand is a french stamp for 18K gold (and it has been tested).

The maker's mark has two letters, "SG" which are divided by a key symbol and all of this is enclosed in a diamond shape. (The S is a bit worn, but I found another similar watch online with the same mark and it was definitely SG.)

The watch is covered in green enameling and has many rose cut diamonds. There is a matching fleur des lis pin or fob to hang it from but must have been added later because it is only 14K gold. It also has rosecut diamonds.

There is a serial number of 38388 stamped in two places.

Do you know who could have made this watch?