Moral reminders can apparently be very effective. I'm reminded of a couple of experiments performed at a university on the university students in a lab where they tested what changes would make students cheat more or less.

In one experiment, university students were asked to sign a copy of the school's honor code before a test, and cheating went down. This, despite the fact that that particular university didn't have an official honor code.

Another example was that students were given one of two tasks before taking a test. In one task, they were asked to recall up to 10 book titles. In the other task, they were asked to recall as many of the 10 commandments as possible. The ones who were asked to recall the 10 commandments cheated less, regardless of their religious beliefs.

So, I suspect that this sign does achieve its intended purpose, to get English speakers to be more careful when peeing.