On a rural road parallel to a freeway you keep passing small roadside signs showing nothing but a seatbelt symbol, in places where a seatbelt reminder makes little sense. What are they really?

Correct answer: A. Emergency detour route markers in the closed position — the seatbelt face is the back of the sign, and they are flipped open when a detour is in use

Folded-away detour markers. Book 8 describes a flip-open Emergency Detour Route trailblazer built from two hinged tabs: "in the OPEN position, the top tab displays the EDR symbol and Provincial Crown, the bottom tab displays the directional arrow", and "when this trailblazer is CLOSED, only the Seatbelt symbol will be visible to motorists. The Seatbelt symbol is installed on the back of the directional arrow tab." So the seatbelt face is simply the back of the sign, and the assembly sits closed until a freeway closure puts the detour route into use, at which point crews flip the tabs open along the whole route. Emergency detour routes exist so that traffic diverted off a closed freeway has a signed path to follow rather than scattering onto local roads.

Source: MTO Driver's Handbook: Ontario Traffic Manual, Book 8 — Guide and Information Signs, Volume 1 (May 2010), Section 10 — Emergency Detour Route (EDR) Signs, EDR Trailblazer B (flip-open design)