There is no umpire manual for signals on the MLB website, interesting
9.02
(a) Any umpire's decision which involves judgment, such as, but not limited to, whether a batted ball is fair or foul, whether a pitch is a strike or a ball, or whether a runner is safe or out, is final. No player, manager, coach or substitute shall object to any such judgment decisions. (s) If there is reasonable doubt that any umpire's decision may be in conflict with the rules, the manager may appeal the decision and ask that a correct ruling be made. Such appeal shall be made only to the umpire who made the protested decision. (n\b) If a decision is appealed, the umpire making the decision may ask another umpire for information before making a final decision. No umpire shall criticize, seek to reverse or interfere with another umpire's decision unless asked to do so by the umpire making it. (c) The manager or the catcher may request the plate umpire to ask his partner for help on a half swing when the plate umpire calls the pitch a ball, but not when the pitch is called a strike. The manager may not complain that the umpire made an improper call, but only that he did not ask his partner for help. Field umpires must be alerted to the request from the plate umpire and quickly respond. Managers may not protest the call of a ball or strike on the pretense they are asking for information about a half swing. Appeals on a half swing may be made only on the call of ball and when asked to appeal, the home plate umpire must refer to a base umpire for his judgment on the half swing. Should the base umpire call the pitch a strike, the strike call shall prevail. Baserunners must be alert to the possibility that the base umpire on appeal from the plate umpire may reverse the call of a ball to the call of a strike, in which event the runner is in jeopardy of being out by the catcher's throw. Also, a catcher must be alert in a base stealing situation if a ball call is reversed to a strike by the base umpire upon appeal from the plate umpire. The ball is in play on appeal on a half swing. On a half swing, if the manager comes out to argue with first or third base umpire and if after being warned he persists in arguing, he can be ejected as he is now arguing over a called ball or strike. (d) No umpire may be replaced during a game unless he is injured or becomes ill.