Yes, I do it as a courtesy to Truckers and Leo's! I'm a retired OTR Truckdriver! A long time ago when I took a CDL test at the DOL that light flashing was a question on the test that I took. I was amazed to find out it is against the law. How do I know this? I answered the question incorrectly and said it was O.K. to flash headlights. The DOL Officer told me if you flash a truck to pull in front of you and a accident occurs from that result, you are responsible for that accident by signaling to the truck that it is O.K. to pull in. I have never in my 44-1/4 years driving OTR heard of anyone being cited for flashing there head lights. Good Question