Aircraft, usually Cessnas or helicopters, which carry electronic signs with lights that flash in sequence. Usually airborne between dusk and midnight, they are most frequent however between 2000 and 2200. Because the advertising plane’s message is clear and legible only when the craft is directly above the observer, it is frequently the source of mistaken UFO reports. Many witnesses, seeing the lights flashing from right to left, assume that the lights continue in around the craft in a loop. Thus they conclude, falsely, that the craft is disk-shaped and possibly rotating. When the message is completely and the last light does out, the illusion is created that the entire craft has vanished.
Flight schedules of advertising planes can be checked by telephoning the individual aerial advertising companies listed in the telephone directly. However, in the United States, some advertising planes fly over several states and the witness or investigators may not be able to trace them through local advertising companies.