How can you tell a traffic signal is a dedicated bicycle signal, meant for cyclists rather than general traffic?

Correct answer: D. Its lenses show a bicycle symbol instead of a plain colour circle

A bicycle traffic control signal is required by regulation to use a bicycle symbol inside each coloured lens (green, amber, red, arranged vertically bottom to top in that order) instead of a plain circular indication — so a small signal head showing a bicycle-shaped outline in the lens, rather than a plain coloured circle, is specifically directing cyclists, separate from the signals facing general traffic.

Source: MTO Driver's Handbook: Book 12, Section 2.7, HTA Regulation 626 Sub-Section 2 — Bicycle Signals