I have a full sized pick up, with a steel box taking up a portion of the bed.
I have used a hitch extender for almost a decade to haul around my 14' kayak.
According to the CHP officer that pulled me over, I am not CA legal as the kayak is extending too far beyond the rear of the truck.
He pulled me over for speeding, not due to the kayak.
After requesting my license, registration and insurance he asked how I came about my flag.
I told him my daughter looked at me a little funny one day when I asked her if she had any old red laced bras I could have.
After that he let me go with a verbal warning to slow down. I have used one style or another of my "red flag" ever since.
