Sign stealing is a dark art, like government spying, it’s both reviled and admired. It used to be the work of base runners on second. Now apparently it seems to have risen to the level front office shenanigans.
It’s pretty common knowledge that former Dodger and current Cubs hurler Yu Darvish reportedly tipped pitches in the 2017 World Series. Picking up “tells” by a pitcher is as old as baseball itself. But sign staling is another thing.
Signs are used precisely to keep the opposing team from knowing your intentions. So those teams and individual players who engage in sign-stealing are scrutinized by opponents and sometimes active countermeasures are used, like in this situation involving the Cubs Javier Baez in 2018 against the Rockies.