FROM WIKIPEDIA
In ice hockey, each team has a designated captain, who wears a "C" on his or her jersey.
The only player allowed to speak with referees about rule interpretations is the captain, or, if the captain is not on the ice, an alternate captain. Goaltenders may not be designated as captains or alternate captains because of the logistical challenges of having the goaltender relay rules discussions between referees and coaches and then return to the crease.
The captain is expected to be a locker room leader and is often considered the primary representative of the team to the public. The captain also represents the players' concerns to the coaches and sometimes is responsible for organizing the team's social functions.Captains are selected by team coaching staff; some teams hold a vote among the players to choose the team's captain. Captains are usually veteran players, though on occasion younger players are chosen. The selection is often seen as an important moment for a team, and one that can affect the team's (and newly appointed captain's) performance.
Some teams rotate captains rather than keep one for an extended period of time.
Teams may designate alternate captains, who are sometimes referred to erroneously as "assistant captains". Alternate captains wear the letter A on their jerseys in the same manner that team captains wear the C.
When the captain is off the ice, any alternate captain on the ice is responsible for fulfilling the captain's official role as liaison to the referees.
Teams need not appoint the same players as alternate captains from game to game, though they generally do. NHL alternate captains perform many of the same leadership and team building roles as the captain.
FROM USA HOCKEY
Rule 202 Captain of Team
(a) One Captain and not more than two Alternates shall be
appointed by each team. In each instance, only one of these
designated players shall have the privilege of discussing with
the Referee any questions relating to interpretation of rules
that may arise during the progress of a game. They should
wear the letter “C” or “A,” approximately three inches in
height and in contrasting color, in a conspicuous position on
the front of the sweater.
(b) The Referee and Official Scorer shall be advised prior to the
start of each game, the name of the Captain of the team and
the designated Alternate(s). This information will be added to
the scoresheet.
(c) No goalkeepers shall be entitled to exercise the privileges of
Captain.