Supt. is the short written form of superintendent. You write it, you almost never say it — when reading aloud, you say the whole word "superintendent." It shows up in front of a name, like Dr. or Prof.: Supt. Rachel Lin. The two places you will meet it are the police and schools. In British and Commonwealth police forces, superintendent is a senior rank, above inspector, so "Supt. Wong" is a fairly high-ranking officer — the sort of person who speaks to the press after a big case. In American schools, a superintendent runs a whole school district, above the principals of the individual schools, so "Supt. Garcia" is an education administrator, not a police officer. Same abbreviation, two different worlds; the sentence tells you which. The capital S is part of it, and so is the full stop in American writing. British writing often drops the stop and writes Supt with no period. Both are correct in their own place. In British police stories you may also meet Ch. Supt. or Chief Supt., which is one rank higher again.

superintendent（警察的「警司／警察分局長」，或美國學區的「教育局長」）的縮寫