Weird signposts appearing around house?

I've had that, and it's related to fencing/gates. Trying to remember exactly, but I think it occurred for me when I had move objects on turned on and sat a gate in the yard while moving fencing. When I would move the gates later, those posts would appear. Someone suggested drawing fencing over the area and then deleting that to get rid of them, which I think worked. For me, for a long time before that solution came up, I resorted to placing trees over them to hide them. :D