Sometimes looking neat is all you need.
On the other hand a real flamer round would probably also be possible.
A flamethrower would be relatively easy. A hard wax round with an igniter that becomes softer during travel (pre-heater? - maybe just air friction) so on impact was liquid enough to stick and burn to the target. Kinda like a realllllllly unpleasant rubber bullet. Would work as a marker as well.
A flamer on the other hand....
Maybe a shotgun shell form factor butane/aerosolised oil cannister under pressure?
Of course the problem is that flamers are truely ineffective weapons (except if you are fighting dried brush
![Smile :) :)](https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f642.png)
) Great for eyebrow removal, but not a lot more.