Not your city our country but i had quite an experience a few years ago regarding large banners.
I went back and forth for almost a month with my city's (Ottawa) Permanent
signs By-law officer and the Temporary
signs by-law officer (yeah two different departments)
Banners did not fall under the permanent
signs department since they do not fit the criteria and since i was leaving it up for more than 6 months it was not considered a temporary
sign either.
So i have it in an email that i keep that is a response from one of the by-law officers stating that they would not act upon it unless there was a complaint lodged by a citizen.
Whenever i get a request for a large banner and the customer asks about permits. They get a copy of my email.
I have a few customers that do not want to take the risk of spending so much money on a chance that someone would complain.
I have however, a very large customer that goes ahead regardless and they have banners that have been installed over 4 years now with no problems.
Nothing to add the the OP's question. Just a story that came to mind reading this.