N545MM is reserved. Post-cancellation hold held by Cancelled/Not Assigned — if it isn't renewed, the FAA releases it on Jan 13, 2030 (in about 3.5 years).
This tail was recently cancelled. The FAA holds cancelled N-numbers before releasing them back to the public.
Reservations lapse more often than you'd think. Check back around Jan 13, 2030 — if the holder doesn't renew, it becomes available. See everything scheduled to free up in January 2030.
N545MM has been worn before. Past registrations from FAA deregistration records:
Tails one nudge away from N545MM that aren't assigned or reserved: