Was looking for this info so figured it might be nice to deposit it here. 
Acceptable N number format
https://www.faa.gov/licenses_certificates/aircraft_certification/aircraft_registry/forming_nnumber/
Advisory Circular describing visibility and formatting guidelines for N Numbers
https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_45-2E.pdf
Acceptable N number format
https://www.faa.gov/licenses_certificates/aircraft_certification/aircraft_registry/forming_nnumber/
Advisory Circular describing visibility and formatting guidelines for N Numbers
https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_45-2E.pdf