Odd signs on highway lamp posts

In Toronto, on certain sections of certain highways, every tenth lamp-post or so (it seems) is tagged with a little sign depicting a fire hydrant.
I always wondered, what do they mean, and for whose benefit are they put up?

Would these signed posts happen to be located near fire hydrants? If so, they’re there to help firemen find the hydrants if they’re buried in snow (the hydrants, not the firemen).

Shiva: The signs are posted on the highways, where there aren’t any hydrants. In many places there isn’t even a shoulder to pull over onto.

The fire hydrants are probably flush with the ground. On a limited access highway, you want to have as fewimmovable objects poking out of the ground as possible.

I’ve seen those signs too. Is there a wall next to the road? Often I’ve noticed that there’s an opening near the sign; presumably it’s for access to the hydrant.

elmwood, I didn’t know about the flush hydrants. They’d simply have cover plates, right?