Yeah, not sure of the safety benefit of these things. The only time I have seen them was in Laos when a couple of Canadians were using them to advertise the fact that they were Canadian - they stuck their ubiquitous Maple Leaf to them (in place of it on their panniers/luggage). I am not sure of the benefits of advertising your nationality in this day and age also....
The only advantage I can see is that you will be visible over a hill/hump, but even then I don't think some drivers will alter their speed or drive more carefully.