I've been coaching for 21 or so years, most of those as a head coach. I've never felt the need to have a sign like this. 1.) I'm not trusting my catcher to call pitches any better than the umpire. 2.) What am I actually going to do with the information? 3.) This is just teaching excuse-making which is something I can not tolerate. 4.) At all but the highest levels of varsity baseball, we're not trying to execute a specific game plan against a specific hitter and even if we were, the chances that a 14yo pitcher and catcher could implement and execute said plan are almost zero.
During the few years I coached state-ranked varsity teams, if my catcher felt we weren't getting a certain spot that we needed, we could discuss that between innings and how to adjust our game plan against certain hitters.