Push Through Letters.
These type of signs have a backer panel with illuminated letters, but they are not individual letters like channel letters. The letters are cut out translucent acrylic, then pushed through the sign. The backer panel is aluminum and the letters are router cut out of it, then the acrylic sticks out of the sign slightly. The light then comes from the backer panel and shines out through the acrylic letters to illuminate them. This is a good type of sign to use when you want a 3d look, need a backer panel, and want the sign to light up.