Rummaging around the public part of the site, I've noticed that game suggestion, writing partner wanted and related thread types often have headers with abbreviations in square brackets.
It would be helpful to newcomers if there were a sticky with interpretations of the common ones (surely the meanings can be described in PG-13 rated language, even if the content of the thread being advertised would be NC-17).
M/M is obvious. I'm guessing NC is short for NC-17, but what does MUL mean? and there are others that are similarly mystifying.