I am trying to find out more about my grandfather's Regina pocket watch (photos attached). I have done some online research but haven't found much more than the history of the Regina/Omega company and the age of the watch. He passed away in 1935 so the 5,000,000 series date range of 1916 to 1927 makes sense. The watch has a crest-shape on the back. Is this just space for possible engraving? The watch chain has a small skull and crossbones with coloured stones for eyes on one end. What is the significance of this? It has the original box and guarantee booklet. I don't understand the six-digit number in the booklet (#371927). Would this be the movement number? Any other comments on the history, background, or research sources would be appreciated.