Just how dumb are catchers and pitchers? It is down to stubbornness, laziness or dumbness that all catchers signs dont have changing pre-decided indicators that change the signs or the sign order with todays technology. You base it on inning number or the score or number of outs or anything else that changes as the game progresses. It would completely foil any sort of sign stealing, legitimate or via technological device.
Freegards
They can use Play Call Signs in football, that the other team can clearly see, but obviously they don't seem to be an issue.