Does it make you uncomfortable if a gentile places a pebble on someone’s grave?

I’ve long held this to be a meaningful tradition of beautiful symbolism, and on some occasions when visiting the grave of an estranged loved one or someone I looked up to, I’ve been tempted to put a pebble in order to remain with them a while, physically and in thought. However, I’m not Jewish and neither are some of the people whose graves this would apply to. Would it be breaking any rules, or making people uncomfortable, or in any other way generally icky if I did this? I know it’s part of a mitzvah of burial/remembrance (?) and might not be something I should be allowed to participate in as a random agnostic.