"Carl R. Stevenson" wrote

4U1ITU is the station of the International Amateur Radio Club at ITU
HQ in Geneva ... I've operated the station. The significance of the
prefix is that 4U's are UN callsigns.

I'm not speaking of the ITU but the IARU (not the same thing at all). The
IARU HQ station is not associated with the UN (nor the ITU) so does not have
a "4U" prefix.

73, de Hans, K0HB