So to avoid this confusion, I recommend putting tags on a mafia game in sign-ups to make it more easily distinguishable. Tags such as ++ on each end should work. Example:
++20% Cooler Mafia [4/20]++
This would easily be recognized as a game in sign-ups, and plus it saves the trouble of having to write "In Sign-Ups" (although you still could if you wanted) and saves time because then new players won't have to read the whole title to know which games they can join. And the less confused new players are, the more players that will come.
Also, it'd just look cool to see ++ on the joinable games, and it would attract attention to those games, maybe even making them fill up faster.
TL, DR: Put ++ tags on your game in sign-ups, like this:
++In Ten Seconds Flat Mafia (10/15)++
-SG7 (
![Cool 8-)](./images/smilies/icon_cool.gif)