Canada's history is peppered with interesting road-sign standards that deviate from their stateside counterparts. Some of the best examples are the blue signs that were formerly used to denote school crossings and school zones.
After two years of living in Ontario, I've come across exactly two of these:

This one is north of Sault Ste. Marie, not far off the 17. Strangely the sign has the notation "Town of Oakville/Owl-Lite 2001" in the margin, which means it's posted 700 kilometres away from the place that made it!

Meanwhile, a specimen of the rectangular "school crossing" variation turned up at Lakehead University in Thunder Bay.

Blue signs have been around for quite a while: These scans hail from a copy of the Ontario Motor League Road Book I tracked down from 1956. (This also means that Canada had schoolhouse-shaped pentagonal signs and graphical school crossing signs 15 years before the US!)
But how
rare are blue signs on the roads today? I've seen none in southern Ontario.
Moreover,
when did the standard change from blue to blah yellow-green?