A little bit of searching on pinterest will stumble you across ceramic mugs (some of them "from the dollar store!") having been decorated with sharpies. The ink is sealed to the mug in the oven, and everyone has adorable mugs.
A bit more searching - for detailed instructions - will inform you that this is BUBKUS. The general instructions: color, bake at 350, wash. The result: washed off sharpie.
I forged ahead.
Well, Baz did.
Then I lined a cookie sheet with parchment.
Here's what I did that's key: I put the mugs in the oven and THEN I turned it on. I baked them at 400 for 30 minutes and then I turned it down to 325 for 15 more and then I turned the oven off and let them cool in the oven.
The colors faded, but they're still there.
So there you go. Go forth and sharpie your mugs!
Oh, and these are the mugs I used. They are awesome.