I am making a car cake and road. I want to have a billboard. What is the best to use for the sign?
I would suggest MMF (marshmallow fondant). The recipe is here in the recipes section. Make your signs 3-4 days out so it can dry and become sturdy. (you can also buy premade fondant to use)
If it needs to have specific logo on the sign I will apply an edible image to the fondant. Otherwise you can write on it with edible ink or icing.
How tall do you want the billboard to stand? I made a 4x4 cake not too long ago and used gumpaste and a candy stick for the creek sign.
My sign was about 3 inches tall over all. I stuck the brown gumpaste around the candy stick then shaped into a board sort of look. I made the actual sign separate. When both parts were dry I glued them together with gumpaste/water mixture. I can give more information or a closer picture of the sign if it's helpful to you.
I like the sturdiness of candy clay over fondant or gumpaste. I find that it takes less time to dry, and is easier to mold (it holds its shape while working). I use it for trees, signs or what have you to make them stand with little support!