Mind is a four letter word.
"Mind your P's and Q's." It is one of those sayings that has always been a bit odd to me, yet the explanation for it (or at least one explanation for it) has had a most satisfying answer to me. When doing typesetting (using actual metallic moveable type), the letters were the reverse of how they'd be printed and had to be placed in the typesetter reversed as well. A lowercase "p" and a lowercase "q" could easily be confused, so the saying is a reminder to pay attention to details, an aspect which always appeals to me.
And it sounds nicer than reminding you to mind your B's and D's.