I was struck by this sign in Greenville, SC. It had the red circle and also said "no" and "don't", but with the addition of a few more words, made it seem much more positive and pleasant.
Even their "no skateboarding" signs were artistic and less harsh than most:
There are certainly times when behaviors are prohibited or discouraged and signage needs to be in place. But don't let your sense of hospitality or courtesy be negated in the process. Make it a sign of your service to put thought and design into all you communicate.
-- dr. beth triplett