What is allowed to be placed on the Graves

Question :

I have seen a number of graves that had the following descriptions: Some graves have one Rakizah (erected stone) placed on them at the front of the grave. On some other graves the people place two erected stones: one at the front of the grave and one at the back of the grave. On the third type of grave the people put three erected stones: one at the front, one in the middle and one at the back of the grave. What is meant by the word Rakizah is a stone that is embedded (in the soil of) the grave. Some people call it Nasibah (that which is erected), because it is erected over the grave. I would like a clarification of what thing is permissible to be placed on the graves of the men and the graves of the women.

Answer:

What is legislated after burying the deceased is that only two bricks be placed erect at the two ends (edges) of the grave. This is so that it will be known that it is a grave even if it is in the center of the graveyard. There is no difference between the grave of a man, the grave of a woman and the grave of a child. No more than two bricks may be placed and there is no harm if a stone or something similar is placed at its (the grave's) side so that it will be known by it and the grave may be visited and so forth.

Source:
Ash-Shaykh Ibn Jibreen
Fatawa Islamiyah, Vol. 3 Pages 83-84