My doormat doesn't say "welcome" either, because I really do try to deter people from entering my private home.
I live in a condo where a lot of the doors look alike, and most of my neighbors are tourists. So I have small sign on my door knob that says "STOP! This is NOT your room!" because countless times folks have just walked right in, thinking it's their room.
I do lock my door 97% of the time, but there are times I forget. The sign has worked amazingly well since I put it there.