Mode S
Below there is a link to the application form for granting the MODE S identification code for your aircraft:
Application for aircraft MODE S transponder ICAO code (AIR.OBR-127)
Assigned Mode S ATC Transponder ICAO identification aircraft code shall be entered into device (transponder) as soon as possible. At de-registration of the aircraft from register of the Republic of Slovenia Mode S ATC Transponder ICAO identification aircraft code shall be deleted from device (transponder). Entry and deletion shall be properly documented.