When Americans visit London and take their first Underground ride, they are surprised and a bit confused by the ubiquitous recorded announcement to "mind the gap." It refers to the space between the edge of the door and the edge of the platform. If I recall correctly, some of the station platforms are curved, meaning there really may be a gap.

This isn't public transit. It is the side of another Mexican restaurant on Cherokee Street. Of course, it refers to social distancing but if you have never been to London the meaning would be lost.