can't say I have ever smoked herb with cops but had a few intresting situations with cops.
First, me and my old friend back when i was a teen came around the corner smoking a blunt in nyc to find two cops on horses standing there. So i palmed the blunt and asked them for directions to someplace i didn't need to go lol.

Another time we wanted to grab a bag of herbs before we hit the club, my friends started freaking out on me because there was a cop standing a few feet away when i was making the deal, so to further their freaking out, i handed off the cash and took the bag into my hand in a single motion, walked over to the cop, and asked him if he knew if the park restroom was open still, my friends nearly had heart attacks..