One thing I recall about a 1970s Mad Magazine issue is once in the letters section they had a picture of an envelope they received at their main HQ in NYC which was addressed to them SOLELY with a cut-out picture of Alfred E. Newman. NO address at all, just AEN's face and a stamp. I think the letter came from a mid-West state. - EDIT: it was the 1970 one below from Washington.
In the 1980s I had season tickets to the Binghamton (NY) Whalers ice-hockey team. Inspired by the Mad mag story above, I once mailed my check to pay for the season tix and just put a stamp and a picture of the Whalers logo on the envelope. I knew they must have gotten it as the check was cashed and my tickets were ready.