I've been lucky enough to visit the great city of London and I was quite taken with the Mind the Gap slogan used on the Underground. It is a warning that is clear without being wordy. It is a direction to the passenger, expressed in three short words. I'm sure that we could do with more such pithy directions.
I have a magnetic version in my office at work.
It reminds me of holidays in foreign places, which is pleasant, but it also reminds me that gaps exist wherever one service meets another (in the case of the underground where the train meets the platform). Sometimes you can't make the gap disappear and have to give the passenger a timely warning.
Connecting systems is an essential part of what we do at work. We automate and smooth what we can but it is the bump between systems that is the hard work and it is us who have to mind the gap as best we can.