A.R.
My son did the same thing, only he did it with others too (mostly ladies he was close to like his babysitter and grandmother - thankfully they were patient with him). I would take his hand out and tell him "no, we don't do that" and kiss his hand, which I would then hold or put someplace more acceptable. Over time, he would just put it on my shoulder or ask me to give his hand a kiss - I think it was less about attachment to my chest as it was about the skin to skin contact and warmth. Over time, it will stop - but if you let him do it at home he will want to do it everywhere...