Q. What is the reason for placing small stones on the matzeiva after the unveiling ceremony? If you can’t find any stones, is it permitted to take some from another kever or is that stealing?

A. The S’hloh, (Rosh Hashana) Eliahu Rabba (224: 7). Be’er Heitev (O.H. ibid. 8) mention the tradition and explain that the reason is honouring the niftar by leaving a mark that shows one visited the kever. They also mention that even leaving some grass leaves is acceptable.

Horav Shlomo Miller’s Shlit’a opinion is that even if one may not transgress the prohibition of stealing by removing a small stone left on another matzeiva, as the one who placed it there may not have had the intention of acquiring it when he pick it up and he is also leaving it in a place that is open and hefker, it is still improper to do so.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a