This sign is made of plastic rather than aluminum because:
1) More durable than aluminum where vandalism is a concern (can bend without forming shape or cracking like aluminum).
2) Safer. Because these signs are used for parking garages or pedestrian walkways where there are low ceilings and limited mounting space, these plastic signs provide less risk for serious injury. There are no sharp edges for occupants to walk into or scrap themselves with.
3) Will last longer in wet or damp conditions compared to aluminum.
4) Acceptable for Toronto's Mun. Code Schedule A-1 to Ch.629 (Safe-Exit Alert Sign) in any material.