Sorry, I'll try to collect my thoughts better here,
182 (2) states you must obey the instructions of all signs errected.
So, what sign did I disobey? "forbidden left turn"
All signs in the HTA have specific definitions (as law should). Highway traffic act defines Signs, including "forbidding left turn" under Signs (9)
Signs
(9) The provisions of this section are subject to any sign, as prescribed by the regulations, forbidding a left turn, right turn, through movement or combination thereof that is posted at an intersection and every driver shall obey every such sign. R.S.O. 1990, c. H.8, s. 144 (9).
So, "forbidden left turn" signs have a clear definition of "that is posted at an intersection".
Wasn't posted at an intersection, did not disobey the defined "forbidden left turn" sign as defined by the HTA.
It's like if they said, "everyone driving a red sports car" instead of "that is posted at an intersection".
Signs
(9) The provisions of this section are subject to any sign, as prescribed by the regulations, forbidding a left turn, right turn, through movement or combination thereof that is posted while driving a red sports car and every driver shall obey every such sign. R.S.O. 1990, c. H.8, s. 144 (9).
I wasn't driving a red sports car (disobeying the sign at an intersection) - so I wasn't disobeying the sign.