A Notice to Airmen, a.k.a. NOTAM, is a notice filed with an aviation authority to alert aircraft pilots of potential hazards along a flight route or at a location that could affect the safety of the flight.
As by ICAO Documentation 9432 – manual of radiotelephony, a callsign shall be one of the following types:
On initial contact, pilot must spell his complete callsign, usually at the end of his message. Always pronounce each digit separately.
A pilot shall use his abbreviated callsign only after air traffic controller has taken the initiative.