Most standard outdoor signs are made from 4mm, white, polypropylene plastic corrugated. It may not be adequate is in high winds, large signage, below-freezing temperatures or used in the display as a support panel. In these circumstances, you may need to add a frame, additional fastening points for the sign, using PE material or thicker and heavier material.
If UV color fading is an issue then better to stay away from red, orange or yellow material. Silkscreened printing, especially with UV inks, is recommended. If needed, UV additive can be added during the extrusion process of the sheet.