You weren't charged against the "Ontario Traffic Manual". The Ontario Traffic Manual Books and/or the Official Government Driving Handbook are simply guides. OTM for traffic practitioners and the Handbook for new drivers. They are not a defense to Highway Traffic Act violations. If you have an issue with the information provided in these guides, consult the many names listed in its credits and maybe they'll consider an addendum in your honor.
Open up a Government Drivers handbook and it will tell you "As you read, remember that this handbook is only a guide... For official descriptions of the laws, look in the
Highway Traffic Act of Ontario and its Regulations..."
You were charged under the Highway Traffic Act and it tells you everything you need to know about sign placement. The Highway Traffic Act states:
2. (1) Subject to section 4, where a maximum rate of speed other than that prescribed by subsection 128 (1) of the Act is prescribed for a highway in a local municipality or built-up area, speed limit signs shall be erected on the highway, in each direction of travel,
(a) not more than 600 metres apart where the speed limit prescribed is 60 kilometres per hour or less; and
(b) not more than 900 metres apart where the speed limit prescribed is greater than 60 kilometres per hour and not more than 70 kilometres per hour. R.R.O. 1990, Reg. 615, s. 2 (1); O. Reg. 175/08, s. 1.
(2) Where the maximum rate of speed for a highway in a built-up area more than 1,500 metres in length is that prescribed by subsection 128 (1) of the Act, speed limit signs shall be erected on the highway not more than 900 metres apart. R.R.O. 1990, Reg. 615, s. 2 (2).
(3) Where the maximum rate of speed for a highway in a built-up area 1,500 metres or less in length is that prescribed by subsection 128 (1) of the Act, speed limit signs shall be erected on the highway not more than 300 metres apart. R.R.O. 1990, Reg. 615, s. 2 (3).
There is no requirement listed in The Highway Traffic Act that states a sign must be placed at every intersection.