Thank you sir Voyager!
Actually I thought of it just like a metamorphic rock (maybe of gem quality) of some sort so I took a picture and then when I reviewed, I was surprised to see that it looks like a heart. I agree sir with you that it is probably a marker, maybe below or points towards something. I noticed too the lines and circles on the rock but the area just undergone some major construction since 2006 so I will still ask the owner if this was moved or anything.
I am more interested if this rock bears something inside as it is color pink.