I'm in Lake Jackson, TX and a state trooper followed me home from the gas station, just a few blocks. He said he wasn't pulling me over, but he wasn't sure about the flashing rear lights be legal, then he left. I checked the Texas Transportation Code and there is nothing in there about flashing tail lights. Also, no mention of it during my annual vehicle inspection.
So, you are good to go, flash away.
. I keep a copy of the relevent part of the Transportation Code in my glove compartment, in case I get stopped again by a curious trooper.