The following registration marks must not be reserved for, or assigned to, an aircraft:
(a) the registration mark of an Australian aircraft;
(b) a registration mark that has been reserved for an aircraft under regulation 47.145;
(c) a mark that has been assigned to a dealer;
(d) a mark that might be confused with any 5 - letter combination used in Part II of the International Code of Signals;
(e) a mark that might be confused with any 3 - letter combination beginning with Q used in the Q Code;
(f) a mark that might be confused with the distress signal SOS;
(g) a mark that might be confused with an urgency or safety signal.
Examples: Of urgency or safety signals
XXX, PAN and TTT.