"You can observe a lot just by watching." -- Yogi Berra
Stealing signs sounds like something a bunch of delinquent kids might do late on a weekend night to alleviate boredom -- back before World of Warcraft was invented, anyway. Applied to baseball, however, stealing signs refers to the gray-area practice of intercepting the opposing team's body language signals and using the information to counter your adversary's tactics.
There seems to be some confusion as to whether this one is properly considered "cheating" or just being observant of your surroundings. The closest thing to a definitive answer is, "it depends." In the most common scenario, a runner on second base watches the well-choreographed movements of the opposing team's pitcher and catcher, attempting to crack their code of what pitch will be thrown next. The man on second, in turn, figures out a way to communicate this to his teammate who is up at bat.
Pitchers don't appreciate this silent eavesdropping, and they might retaliate by "accidentally" hitting the opposing batter with a throwaway pitch. Stealing signs as just described isn't exactly forbidden, officially. Lots of players do it. The idea, though, is to do it artfully and without getting caught.
Sign stealing becomes more morally fraught when people or equipment outside the diamond enter the act. It's considered highly unsportsmanlike for people in the dugout or the stands to steal signs and use that knowledge to help the person at bat. The Toronto Blue Jays found themselves amidst controversy in 2011 when a mysterious "man in white" in the centerfield seating area was reported to be using arm signals that correlated with specific pitches. Blue Jays players and management, naturally, denied any involvement [source: Nelson].
MLB is more specific when it comes to using "equipment" to steal signs, reminding teams each year that use of items such as binoculars, telescopes and video equipment to interpret other teams' signals is off-limits.
Some of baseball's most colorful stories involve the practice. The 1951 World Series-winning New York Giants allegedly won that pennant with the help of a sophisticated, electric buzzer sign-stealing system. It was a story that would not attain widespread public knowledge until nearly half a century after it happened [source: Prager].