The JewishGen'er, who is a Yeshiva student, wrote, "Just one small correction : the photo on which you click to get a better view of the 'tombstone' is actually not a tombstone. The Hebrew writing is the first words of the first five of the Ten Commandments. It is very common to have two tablets, looking exactly like the one in your picture, above the Aron Kodesh (Holy Ark) in a synagogue - symbolizing the Two Tablets on which the Ten Commandments were written (five commandments on one and five on the
other). To the best of my knowledge, the Ten Commandments were never placed in a cemetery. My guess is that this 'tablet' was taken from the synagogue, probably during the Holocaust, and left out in the Jewish cemetery. If  I'm correct, you now have evidence of the synagogue!"