I’m with missileman on this issue. I’ll use then whenever I feel it’s necessary for safety and I don’t care what the “rules” are.
I had a throttle cable break on my motorcycle long ago and was stuck with an idling engine. I was able to limp home by turning up the idle speed adjustment to a fast idle. This allowed me to go 20-30 mph on the shoulder of the highway. This was one of the situations I turned on the emergency flashers.
If you have a good reason for using them, it would take a real Barney Fife on a power trip to ticket you for using them even if it is technically not legal.