A sign at the curb reads LOADING ZONE and shows a truck symbol, with an arrow at the bottom pointing to the right. You are in an ordinary car and want to leave it there while you run into a shop. May you?

Correct answer: D. No — parking is prohibited in the direction of the arrow except for loading or delivery, and the truck symbol limits even that to commercial vehicles

No — that sign carves out an exception you do not fit. Book 5 says loading zone signs "indicate that parking is prohibited in the direction(s) indicated by the arrow, except for the specific purpose of loading or delivery activities." There are two versions, and the difference matters. The LOADING ZONE — COMMERCIAL VEHICLES sign (Rb-122A) applies "except for the specific purpose of loading or delivery activities by commercial vehicles", while the LOADING ZONE — GENERAL VEHICLES sign (Rb-122B) opens the same exception to "private or commercial vehicles." Either way the exception is for loading or delivery, not for parking while you shop. The arrows are not decoration: they show which direction along the curb the restriction runs from that sign.

Source: MTO Driver's Handbook: Ontario Traffic Manual, Book 5 — Regulatory Signs (December 2021), Section 13.2 — LOADING ZONE Signs (Rb-122A, Rb-122B)