I don't know what to make of it, it really is strange. Obviously, the Yankees and Red Sox are paranoid about the Jays doing something. The fact that they use multiple signs with nobody on base speaks to this fact. They both have had players play for them that have played for the Jays and the Sox have the Jays former manager. So if nothing was going on, they would know nothing was going on, and there would be no reason to continue being paranoid. Or perhaps something is going on, and they do know about it, but if it's something inappropriate, why not involve major league baseball and make a big stink about it?
Do the Yankees and Red Sox do this against the Jays in their own ballparks? Do they do it with other teams, or just Toronto? I've made a mental note to watch for these things, but I always forget.