You can decorate the top of the galette with any pattern. I did some with a lattice-work pattern but then my daughter remembered we had a crown-shaped cookie cutter, which we used to make imprints in the top.
I presented each galette with a crown on the top. Whoever found the fève got to wear the crown. I found some at Hobbycraft that were thick foam with gold glitter and which were fully adjustable. They are sturdy enough that we'll be able to use them again next year.