I apologize for having to edit this post but I was asked by a family member to remove the story behind the stamp. The question still remains on whether there is a grill. I appreciate the responses and will try some of the suggestions. thank you.
Interesting story! Sorry to hear about your families loss, situation aside.
I see what Don is talking about but, a better photo might help.
A few years back, I found out a cousin of mine was a stamp collector via the listings of recent deaths in the APS The American Philatelist magazine. I wasn't reading it but the name popped off the page at me. We never knew we were both life long collectors and started as kids. We only saw/talk every 10+ years or so, I guess it just never came up.
Like the others, I think I see a grill there. The cancel on the front appears to show the grill pattern, too.
Have you tried dipping it in watermark fluid? Sometimes a grill will pop right out at you in fluid. Plop the stamp in, and see if it is apparent as the stamp soaks up the fluid (as it is 'wetting') let it sit a bit (sometimes things are more apparent after it has had the fluid soak all the way into the paper fibers), and lastly take it out and watch it as it dries (different parts of the stamp will likely 'dry' at different rates, and a grill may pop right out at you as the last of the fluid dries).
Somebody suggested shining a light at a glancing angle on the back - anything sticking up (or dented down) will be easier to see.