So for the person on a roof this would depend entirely on the roof your on. If you find a rooftop resturant and simply order lunch there your good to go for example. Looks totally normal. The radios would need to be concealed yes, but theyre not that big. You could fit them in a backpack, or inside pocket of a jacket.

I think it's best used for like a small group of well organized people who manage comms. Like get 5-6 people spread them around the area evenly, and let them be peoples go to for communicating with the rest of the group. Rather than everyone having one. Then you rely on just word of mouth when in the local group. Or you could combine the radios with the briar setup. You send a message over the radio, it gets to all the other radio holders with 1-2 miles, then you use briar to disperse it locally among the crowds.

Hiding a few radios in a big crowd is easy, and having only 5-6 people who need to know the coded language makes it easier too.