When my oldest first started writing a few years ago, his handwriting was so adorable that I just wanted to eat it up. I wanted to save every silly thing that he wrote and keep it in a bubble forever. I honestly can't remember if I originally found something like this handwriting-in-an-ornament idea on Pinterest or if I came up with it myself.
The "how to" is pretty simple -- grab a few plain clear plastic ornaments at the craft store for roughly 50 cents each. You'll also need a couple of sheets of holiday-ish craft paper and some little decorations to fill the ornaments - puff balls, jingles bells, glitter, or whatever looks good.
I just kind of eyeball the ornament for size and cut out a circle of plain paper for the child's message. Then I cut out a slightly bigger circle using the craft paper. The craft paper is a bit thicker than the plain paper used for the writing so I find that the craft paper provides some necessary stability inside the ornament (plus it makes it prettier.)
You might have to experiment with the next part to see what works for you, but I carefully roll the two pieces of paper together so that they'll fit through the ornament's opening and then I use a pair of chopsticks to arrange the papers the way that I want them inside the ornament. Sometimes I find I need to use some glue on a q-tip to get the papers to stay the way that I want them. And I let the kids pick out the decorations that go inside the ornament and drop them in - always a fun part for them.
I always try to let them pick their own messages. The possibilities are endless really. They've used -- "Best Teacher Ever", "Most Awesome Teacher Ever", "Best Bus Driver Ever", "World's Best Grandma", etc.