I'd noticed this before but it hadn't really clicked until I was in a cemetery today that had several graves dating back to the 1800's. I noticed that there was a family there, and I was paying particular attention to the grave of a small child. (I was taking pictures.) I took a picture of the larger gravestone with the inscription and everything on it, but then I noticed a smaller gravestone a few feet in front of that had the same name on it. And then I noticed in front of all the families' graves there were smaller stones in front of them with the corresponding initials.
Does anyone know why this was done? I only notice it in older cemeteries though, I don't think it's ever done anymore.