That was more than likely Tear Gas and not just smoke.
JMHO, they should borrow a Crash Crew Truck from the nearest military airfield, mix a batch of nice indelible dye (Purple or Safety Orange sounds good) to the tank of AFFF / Chemical Firefighting Foam and hose all of those "antifa" slugs down with it.
We were told that AFFF was made out of horses' hooves, but it stunk like blazes (especially when it was warm outside), clung like glue to everything it touched and if we got any sprayed on us we'd just throw away any clothes affected and then take a shower every twenty minutes for the rest of the day to get the foam and the stink to go away. Combine that with a little bright-colored dye to mark 'em for a while and I'd call that a really nice job.....
Oh, yeah. I seem to recall that it was prone to make walking difficult, too.
What fun.
Safety Orange faced, foam covered, stinky, stumbling rent-a-thugs. Just what their mommies wanted to come back to her basement sewing room.
I love your suggestion, with one caveat...there was a wind bl,owing and that stuff could get on nice people, who were coming out of the rally, so it's not a great idea; wish it was.