Good for Something
Maybe it could be a little reminder board. When the two of you are going to sleep and she thinks of something she needs to remember in the morning, she could write it there, so she doesn't have to get up and go look for a piece of paper.
Of course, it would have to be a short note.
Why don't you get that marker off the table over there and give it a try? You could write an example message like "Don't forget - find some real cocks to fill pussy and ass. Not useless!" Or maybe she's having so much fun up there with Jeff, she'll want to come back and visit him...you could write his address, so when she sees your little thingy and gets disappointed, she'll know where to go. She's your girlfriend--write whatever you think will impress her. Around the head, along the itty-bitty shaft, wherever it will fit--you have to make the best use of the little space you have.
Just make sure you don't erase it when you rub that tiny thing.