Sign-stealing is a hot topic in baseball these days after the Astros were caught monitoring and recording activity in the opposing dugout during the postseason last year. Houston was eventually cleared of any wrongdoing, though the incident did bring high-tech sign-stealing into the spotlight.
As such, MLB implemented a series of measures designed to combat high-tech sign-stealing this season. Among other things, teams can not have non-broadcast cameras in the outfield, and each video replay room will be monitored by an MLB official. Stealing signs is not against the rules! Improperly using technology is though. That's what MLB is trying to prevent.
In an effort to further combat sign-stealing, MLB is testing out a new device this spring that will allow the pitcher and catcher to communicate though watches.