Need to Notice

As if 'No Smoking' is not clear and well established, this notice one has an extra and rather polite plea to adhere to that no smoking message.

Cleanliness

Here's a sign which is positivity encouraging cleanliness.  However the sign itself is itself rather dirty.  So it's not setting a standard, default or visual expectation.  It's an authority statement which attracts interest and attention but the visual clues are at odds with the message.