KEYS CUT WHILE "U" WAIT

I just saw a sign which announced that while on a bus. I've always sort of thought that the abbreviated spellings like u for you, ur for you're or your, c for see etc, commonly used by young and some not so young people in text messages and email, were just this: abbreviations. But this cannot be right, at least in the case of the above: the number of characters in "U" and YOU is exactly the same. So what is this sign trying to say? Something along those lines?

I know it's cool and trendy to write U instead of YOU but I also know that there is little justification for writing it on a permanent sign, where typing speed is not an issue. So I'll write U, but to be on the safe side I'll also put it in scare quotes.

(Another observation about the use of scare quotes)