Happy birthday road signs are a fun way to celebrate someone's special day. They can be placed in front of the person's house, on the highway, or even in the sky. There are many different ways to create a happy birthday road sign. You can buy a pre-made sign, or you can make your own. If you are making your own sign, you can use poster board, cardboard, or even construction paper. You can decorate the sign with balloons, streamers, and other festive materials. A Happy Birthday Sign Sticker.