Peter Gammons told an interesting story yesterday:
The Red Sox and Yankees had the dueling Apple watches. One of my favorite human beings to ever play, Chris Young, the outfielder, played for the Yankees in 2016 [actually 2015], came over to the Red Sox, and he told me, "Kind of my idea. I shared the whole Apple watch thing. I got it from the Yankees."
(It's hard to tell whether Gammons says "I shared" or "I started".)
On August 14, 2019, the Globe's Alex Speier wrote an article headlined "Why Red Sox Pitchers Are Looking Inside Their Caps":
In an era when catcher mound visits are finite, and when teams are changing their sign systems all the time to combat increasingly sophisticated sign-stealing, the Red Sox have, in essence, a sign-system cheat sheet inside of their hats.