In hockey, every team needs a captain and alternate captains as they are the only players allowed to discuss penalties and calls with the referee during a game. To make it easier for the officials to address the right player, all captains and alternates must wear a "C" or an "A" on their uniform. There is but one simple rule dictating where that letter is displayed.
The Official Rule
Of the captain's letter, the NHL rulebook only states, "He shall wear the letter 'C,' approximately three inches in height and in contrasting color, in a conspicuous position on the front of his sweater." Also, "Alternate Captains shall wear the letter 'A' approximately three inches in height and in contrasting color, in a conspicuous position on the front of their sweaters." While nothing clearly defines a "conspicuous position," most NHL teams have historically placed the letter on the player's left breastplate, halfway between the neckline and shoulder pad. The NCAA rulebook has almost identical wording: "The captain should wear the letter 'C,' approximately 3 inches in height and in contrasting color, in a conspicuous position on the front of the jersey."
Rules on Captains
The only players not allowed to serve as captains are goalies, since constantly leaving the crease during games to talk with the referees would lead to delays in the game. When he was with the Vancouver Canucks, goalie Roberto Luongo was named captain in all official team media, but could not wear the letter "C" on his uniform. Instead, the team used three alternate captains. Any player not acting as captain or alternate who leaves the bench to discuss a call with the referee is subject to a minor penalty for unsportsmanlike conduct.