In Jewish cemeteries visitors often leave small stones or sometimes coins when visiting graves.

The letters on the grave above are (right to left) Tav, Nun Tsadik, Bet, and Hay which stand for tehe nishmato tzerurah bitzror hachayim, "May his soul be bound up in the bond of life (from Samuel I, 25:29).

These two Hebrew characters, Pay and Nun, are found on many Jewish gravestones.  They stand for Po Nikaver, "Here is buried."

My thanks to Scott Latman for the translation and interpretation.