score:2
The D sign is for any overdimensional (not just too wide) loads.
The "D" stands for OverDimensional and Dimensions excΓ©dentaires, introduced by the national harmonization process (agreed to in 1988 and continues today). The reason is probably the same as why there are more other pictorial signs in Canada compared to U.S., i.e., official bilingualism (and official unilingualism in Quebec). A bilingual "WIDE LOAD / CHARGE TROP LARGE" or "OVERSIZE LOAD / CONVOI EXCEPTIONNEL (or even longer, CHARGE DE DIMENSIONS EXCΓDENTAIRES)" would be confusing and less comprehensible due to space constraints on a sign. A monolingual sign hinders interprovincial and international commerce if Quebec insists on French signs.