From OpenStreetMap Wiki
|The FCC ASR (Antenna Structure Registry) registration number for an antenna site.|
|Used on these elements|
|Status: in use|
|Tools for this tag|
This key is used for specifying the registration number of an antenna site in the FCC ASR registry.
The "fcc:registration_number" should be posted on a sign near the tower, which should make it easier to match up ground observations with what is in the database.