I've just had this compulsion to use twigs to decorate some letters for years, and finally did it. After a couple of tries, I discovered the way that works for me.
I've made JOY and now it's time to make NOEL.
I will most likely sell these as Christmas decor items, but there's no reason why you couldn't make them as just twiggy decorations, using whatever you like as the letter, even your family name or a favorite word.
Here's how I started;
Frozen Pizza boxes are perfect for cutting as letters; the letter can be stylized or blocky, keeping in mind that you'll be covering it completely with the twigs.
The twigs are Syringa josikaea, the Hungarian lilac, which is used as the rootstock for some grafted lilacs. There are many other twigs that would work.
I would pick the type that's straighter rather than wiggly, as this would cover up the painted background better. See more of the twigs I recommend for crafts here.
In this case, the rootstock is renowned for taking over the graft, and growing in a coppice type formation.
I routinely prune these out and burn them, but this year I decided to utilize the nice straight growth. You could also use willow of any kind, or other straight-ish twigs.
I painted both sides of the cardboard letters with dark brown and black acrylic craft paint. See the resources page to buy yours.
Then I cut some pieces of wire so each letter can be hung from another longer twig, if you like, or just hung on a rusty nail.
You can be creative with this and develop your own system of attaching the twigs and wire, but I decided to use my hot glue gun.
It's hard to get the glue to be invisible. In future projects I would most likely keep piling the twigs on, to cover up the thicker glue. Don't look too closely!