Two recent event. Had lunch at a local spot Friday and got chatting with the next guy at the counter. Turns out he fishes and boats out of Wiraton. Asked him if he would recognize the meaning of a red flag with a diagonal white stripe. He said "NO", he'd seen them, but didn't know what they were. When I explained it meant there were scuba divers in the area and he should keep well away, he was quite surprised and said he certainly would in the future.
Then, diving yesterday at Cedar Hill (near Wiarton). We ended up the last divers in and were towing our flag. Heard some close sounding boats, didn't give it a lot of thought, as we were mid dive in 35 feet of water. After we came ashore, we were told that one boat in particular had changed course from well off shore and closed to within about 30 feet of our flag (he was just out of range of the rocks being thrown at him from shore), apparently to better idntify it. I've been working on coming up with a better, more visible flag. I think I've changed my mind and I'll fly no flag at all. IF I go to Toby or some place (US) where flags are required, I'll have it along in my trailer, but I've come to the conclusion it's a target, at least until boaters in general are better educated, so it can stay in there.