BEM

(Did you mean a fanzine by Mal Ashworth, or a fanzine by John Kalas?)

BEM (pronounced "bem"), initialese for that stock stfnal character, the Bug-Eyed Monster, became the first piece of fanspeak to get into a mundane dictionary when Funk & Wagnalls included this valuable word, defining it as "various abhorrent monsters, such as are found in science-fiction."

The phrase came about when Martin Alger parodied the alphabet organizations of the Staple War by announcing, in a letter printed in TWS in August 1939, the formation of the Society For Prevention Of Bug Eyed Monsters On The Covers Of Science Fiction Publications, and later, in January 1941, had a letter published that first referred to the cover-critturs as BEMs. (Though, interestingly, Alger also said that BEMs need not necessarily have bug-eyes.)

from Fancyclopedia 2 ca. 1959
(Alger) Initialese for that stock stfnal character, the Bug Eyed Monster, Symbolic of the "middle period" [starting about 1937] and juvenile type of magazine stf, which stirs up the emotions more than the intellect, performs simple transmutations of known and unknown, and makes few concessions to plausibility. Coined indirectly in the August 1939 TWS, when Martin Alger parodied the alphabet organizations of the Staple War by announcing the formation of the Society For Prevention Of Bug Eyed Monsters On The Covers Of Science Fiction Publications and later, January '41, had a letter published which first refers to the cover-critturs as BEMs. It became the first piece of strictly fan slang to get into a mundane dictionary when Funk & Wagnalls included this valuable word, defining it as "various abhorrent monsters, such as are found in science-fiction".
from Fancyclopedia 1 ca. 1944
Bug-eyed monsters, symbolic of the early and juvenile type of magazine s-f, which stirs up the emotions more than the intellect, performs simple transmutations of known and unknown, and makes few concessions to plausibility.

A Memorable Costume.

At A^2^ Relax Icon, held on the University of Michigan's Ann Arbor campus in 1974, one innovative Stilyagi Air Corps member named Stella showed up in costume as a BEM. To create the monster, she went topless, with a strip of fake fur pasted over each breast for eyebrows.