Kodak Universal Backlit works well; Epson also released their name on a backlit media but I haven't tried it. You can laminate to make the graphics last longer, but often not necessary as signage is rotated pretty regularly. Don't expect archival permanence. Generally the graphics are placed behind a sheet of plexi material so it is protected and backlit. Displays can vary quite a bit in size, illumination, and cost.
Ken