https://en.wikipedia.org/wiki/Mind_the_gap

根據維基，最早是英國開始用。後來新加坡，香港，歐洲開始跟著用。

別的用法有：

紐約
Watch the gap.

Ladies and gentlemen, as you exit, please be careful of the gap between the platform and the train.

澳洲
"Please mind the gap when alighting from the train"

個人喜歡越短越好。