Every book we work on has a folder with a tracking sheet, which helps us monitor the progress of each article in the book—design turnover, developer's pass, edit 1st pass, edit 2nd pass, layout, edit 3rd pass, copy edit, and final approval. Because the schedules for these books overlap, I usually have multiple folders on my desk at one time (currently I have seven). As I'm a visual person, I find it's easier for me to locate which folder I want if I put a big recognizable doodle on each tracking sheet, rather than having to read the handwritten title. Some of these doodles are pretty simple (a dragon's head for Dragons Revisited, a pyramid for Osirion, Land of Pharaohs, and so on). Some of them get a little strange.
The doodle for Blood of Dragonscar is a weird, pallid, white-eyed face with a scythe, as weird, pallid undead play a role in much of the adventure. I had to get more creative with the doodle for the Legacy of Fire Player's Guide, as it relates to Katapesh and I didn't want to confuse it with the folder for Dark Markets, so I made a bit of a rebus (LEGO + C + FIRE = Legacy of Fire). The third is for Beyond the Vault of Souls, and requires a bit of backstory. The author of that adventure is my friend Colin McComb, who wrote for (among other things) TSR's Planescape setting. One of the Planescape adventures was called Well of Worlds, and the cover art featured a man being pulled into a pit by a weird slime creature... and the model for that illustration was Colin. So my doodle for this Colin-authored planar adventure is of Colin-as-art-subject from an entirely different, older planar adventure.