At the end of a period, what does the referee indicate with a raised ball?

When the referee raises the ball at the end of a period, it signifies that the period has concluded. This is an established signal within the rules of football to communicate to players, coaches, and spectators that the time for that segment of play has elapsed, and no further action will take place in that period. The gesture clearly indicates the end of play, allowing everyone involved to prepare for the transition to the next quarter or halftime, depending on the game's timing situation. The other options relate to different situations: a timeout, a score review, or a clock adjustment, each of which would require a different signal or action from the referee.