What must a coach do if they wish to hold a defensive conference at the pitcher's mound?

If a coach wishes to hold a defensive conference at the pitcher's mound, it is mandatory to signal to the umpire for permission before proceeding. This protocol is in place to maintain the flow of the game and to ensure that all players and officials are aware of the situation. The umpire's acknowledgment is essential because it provides a formal recognition of the conference, which helps prevent any misunderstandings regarding the time taken or the intent behind the meeting.

In this context, signaling to the umpire fosters clear communication and upholds the integrity of the game. The other options do not align with the official rules regarding mound conferences. They suggest actions that either do not follow the required protocol or imply an inappropriate response after the conference, which is not part of the established guidelines in baseball. Hence, the necessity of signaling to the umpire is integral to the structure and officiating of the game.