my mums brother died in the 1940's (before my mum was born). My grandparents couldn't afford a headstone, so the neighbours clubbed together and bought a flower holder with 'Peter - Our Friend' on it. well.. it got stolen in the late 80's.
While I was wondering around the cemetry a couple of years back with my mum, we noticed the flower holder on another very overgrown grave. We think what must have happened, is it got moved (by accident?) and some person found it and put it on the closest grave. It had been there all these years, but we were just looking in the wrong places.
I really hope that is what has happened to your marker.
If it has been stolen, then the people that stole it have NO respect for themselves or others.