why a stone is placed on a headstone in the jewish faith when visiting a grave?

Answer 1

It signifies that someone has visited the grave. It is a token.

http://www.myjewishlearning.com/lifecycle/Death/Burial_Mourning/TombstoneUnveiling.htm

Answer 2

It is customary, before leaving the gravesite, to place a small stone on the marker to indicate that someone has visited the grave. This tradition may also reflect the biblical practice of marking the grave with a pile of stones. Or, it may be the end result of the custom of writing notes to the deceased and pushing them into crevices in the headstone just as notes are pushed into the Western Wall in Jerusalem. When no crevice could be found, the note was weighted down with a stone. In time, the paper disintegrated or blew away leaving only the stone. Thus, some began to think that the leaving of a stone was the custom... and so it became the custom.

Answer 3

Stones were traditionally placed on graves as a mark of respect- it showed that people had been there. It also served an important purpose: Coming into contact with a dead body, or a piece of a body larger than a figure bone renders a person (tamei) impure- and, if a kohen, from being able to offer sacrifices or perform any other duties of a kohen. It would also prevent someone in such state from participating in sacrifices- such as sin opfferings, the Pesach sacrifice, thanksgiving offerings, going up to the temple to during the shalosh regalim (three pilgramage festivals) etc. Thus knowing where graves are is important, more so in the past than now where graves were not necessarily in segregated graveyards, and had to be clearly marked to make sure they were not mistakenly plowed under, making it impossible for a kohen, or somebody on their way to perform holy activities, to cross the field. So the stones left behind by visitors formed a cairn that clearly marked the grave.

Today, it is a mark of respect, a permanent token that the person is remembered and not forgotten.

Answer 4

We place a small stone upon the gravestone as a sign that we were there -- not so the person who passed away will know, for their soul already has awareness. But so that we will know. We, who are physical, need physical acts to express the reality that we are indeed there. The stone is the "calling card" of the visitor. Flowers die, but the small, simple stone, a symbol of eternity, represents our eternal devotion to upholding the memory of our beloved. Our connection lives on and will never die.