To enter a rehearsal mark at the current bar, select Bar from the Display menu. Set the Rehearsal Mark option to Yes.
The rehearsal mark appears above the first track when displaying in Score mode and above each track when displaying in Single Track mode. The rehearsal mark is a letter enclosed in a box. The letters start with A, and after Z, if there are more, continue with AA, BB, etc. The letters for rehearsal marks are calculated automatically, so if you get rid of one or enter a new one between two old ones, all rehearsal mark letters are adjusted.