What does the down peace sign hand greeting mean?

My husband just recently purchased a Harley. We live in Texas. I have become more aware of bikers while I am driving now. I have noticed(esp. Harley riders) will sometimes make a peace sign pointed down with their left hand. I looked it up online and I got several different meanings: ride safe, peace on the road, keep the rubber down and the shiny side up, 2 wheels down, just me and my bike, or just an acknowledgment of another rider esp. one riding the same brand and style. What does it really mean or could it mean any of those things. That's what I'm beginning to think. Whatever you want it to mean. Am I right?