The late 50s does not seem that historically long ago to me, and I remember my father telling me about a sign on a hospital door in Toronto (where he was a new immigrant) saying "No Irish" at the end of an advert for a job.
So when I was a kid in 1971, it was no wonder I loved the anti-establishment song "Signs" by the hippy Ottawa group Five Man Electrical Band. In their song, most signs were a bad thing, as they usually had a negative aspect about them.
Since then, however, I have come to enjoy various signs which catch my attention for their good advice - as in this manipulated sign which appeared in Austin Kleon's book Steal Like an Artist,
their positive affirmation (though this may be graffiti - I am not sure as I found it on the Cass Art facebook page),
charming double meaning (this is a road sign at Nice airport taken out of context, but appropriate to my recent bad experience with French train service),
and/or just plain old surreality! (I know I posted this Dublin sign before, but couldn't resist doing so again.)