You may find the phrase 420-friendly often in personal ads, especially on Craig's List.
It refers to the term 420 which has become lingo smoking pot.
See the definition of 420
"420 originated at San Rafael High School, in 1971, among a group of about a dozen pot-smoking wiseacres who called themselves the Waldos"
"Hey, is this party 420 friendly?"
You better be careful, those highway police are definitely not 420 friendly. They put their nose right up to you.