Interesting thread. I had never heard of the left two-blink signal. I have some trucker friends, I'm going to ask them if they use it or have heard of it.
These days, as someone posted earlier, so many vehicles have a 3 blink "passing" signal available by a quick touch of the blinker control that I wouldn't trust a two-blink signal as allowing a following vehicle to pass. I would assume someone just touched their turn signal quickly and is about to, or already, pulling out to change lanes.
What is a shame these days is that most truckers don't seem to flash their running lights much anymore signaling "thank you" when you let them pass or pull in. When I first started pulling our camper - not that long ago, 15 years - truckers would routinely say "thank you" with their running lights. I kinda miss it now!
