I’ve looked through my various resources and I have found a few more photos of the mystery sign in Port Rowan that I wrote about earlier this week.
My CNR survey of the area shows this sign, and notes it’s at “894+57” – which translates to “MP 16.94”, so it would make an unusual milepost marker. I think we can rule that out.
Ideas welcome, as always. Meantime, I’ll keep looking through my resources to see if I can find a shot of one of these signs elsewhere.