2 yr old SOS

My 2 yr old son, in social occasions usually hit or pinch other toddlers. This is actually his way of saying 'hi'. After pinching and hitting, he would be quite lovely with the other kids which dont usually happen because some parents just snatch their kids away when my son pinches their children's cheeks. It is quite humiliating for me as I feel judgement on their part. How do i encourage my son to communicate politely with other children?