Crossword puzzle building in Lviv, Ukraine [street art]. You'll have to wait till nighttime, when the combination of the installed lighting system and the fluorescent paint fills up all the boxes with the correct answers.
I can do this with the Sharpie idea. Sharpie design on mug, bowl, plate, or any other oven safe glass object! 350 degree oven for 30 min, and there you have it! Instant art to display your tea + coffee + yummy food in.