This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.
From Bob Kaplow:
(Note - This isn't really a FAQ but a favorite of mine. AE)
The all time classic has to be Bob Sanford's Best MidWest Qualified
Flight winner at NARAM-29. We were flying B Eggloft (don't recall off
hand if it was altitude or duration). He came to the checkin desk with
a model and pre-taped motor. All the Check in officer (Ric Gaff) could
see because of the tape was the "6-2", but being a nice guy, Ric let
him thru, and wrote "B6-2" on the flight card. Well, the model just
barely cleared the rod and pranged. Upon post flight examination,
under the tape where the "B" should have been was...