Update: found out I was brushing the wrong way for 6 months, and a soot stain on a mirror in Akron is what tipped me off
Client had a mirror leaning by the fireplace. I did my usual sweep, packed up, and she pointed at a gray smear creeping around the mirror edge. Never saw that before. Turns out I was pushing soot into the room instead of pulling it up and out. My old brush angle was all wrong. She just smiled and handed me a coffee. So what's the tell for you all, a stain like that or smoke backing up?