No apologies necessary AVM288, I appreciate all the inputs I can get. And yes, there is what looked to me like an "f" between "his" and "mark" on the document, but I didn't know what this was or meant. Now I can see clearly that it is an X somewhat angled backwards. Regardless, and as you and Justin pointed out, now I know that "his mark" means the handwriting on the document was not my great-grandfathers.
And Justin, yes that's extremely useful information on the burials of Colman and Sarah. I did see the record of a Colman Diamond in 1940, but didn't order the death certificate because of my past bad luck in spending money and coming up wrong. The fact that Sarah is next to him clinches this. Where did you get the burial plot information? Would there be any useful information on the death certificates, were I to order them now?