Is it respectful for a non-Jew to place a stone on a Jewish person’s headstone?

I’m a bit of a history enthusiast and I sometimes like to visit the graves of interesting people. There’s a somewhat well known Jewish scientist (Louis Slotin) buried in my city and I’d like to visit his grave. I’ve seen pictures of it and other people have left stones, but I was wondering if it’s appropriate for non-Jews to do so. Is there anything else I should do to be respectful when visiting a Jewish cemetery or a Jew’s grave?