All the recent talk of Marathon cheats reminded me of an ancient issue Computer Gaming World that included "1001 Cheats & Tips". On page 76 the 485th (4+8-5=7) cheat is for Marathon I and II (Macintosh), "At the new game scene (sic) press Command-Option, then start a new game. Then type BUIHAVENOCLUE. Type slowly-type a letter, then wait two seconds before typing the next letter."
The first half of the cheat of course is well known but what are the origens of the second half? A quick google search of "BUIHAVENOCLUE" turns up 13 pages that reference the same cheat. I have included scans of referenced page and a close-up of the specific cheat. For reference they are from the February 1997 NO.151 issue of Computer Gaming World.