Parashas Bamidbar · Passuk 3:39
All the Levites who were recorded, whom at GOD’s command Moses and Aaron recorded by their clans, all the males from the age of one month up, came to 22,000.
Chabad.org — English translation + Rashi
Source: Bechoros 5a.
English: “And Aharon” — it was taught: Why is there a dot over Aharon? Because he was not included in that count.
In context: The dotted letters indicate that Aharon himself was not numbered among the 22,000 Levites; the midrash offers reasons of honor or of status.
Custom
Chazal explain the dots over “Aharon” as signaling that he was not part of the Levitical total.