Tipping Pitches or Stealing Signs

Courtesy of Twinkie Town. Whoever posted the video is calling it "cheating." Does anyone know if this is actually illegal, poor form on Joe Mauer's part, or just a clever way for Mauer to help the Twins out? I know A-Rod was accused of tipping pitches to opponents as some sort of supposed you-scratch-my-back-I'll-scratch-yours ruse to get pitches tipped back to him -- and abetting the other team definitely seems to be against the...