Ontario Highway Traffic Act

Driving south on Bathurst, south of Adelaide.
Realized that could not turn left on King due to rush hour.
Did a U-turn on Bathurst to get back to Adelaide.
Pulled over at corner for "doing a U-turn" on Bathurst.
Ticket offence: "Disobey sign".
Are there "No U-turn" signs on Bathurst? Is this a blanket law - no U-turns on main roads? (How do the ...