On Peugeot and Citroen (PSA Groupe) vehicles, certainly up until around 5 years ago, the heated door mirrors would come on when a DPF regen was in progress. This I understand was part of the DPF regen design, to increase load.
Some owners, wired a small LED in the door mirror to show a DPF regen was underway, so a glance there and you'd know.
No tell tale light would illuminate on the heated mirror button, as it would normally, but the mirrors would be hot to touch and the LED was a quite a clever way round not having any indication of a DPF regen in progress.
I cannot understand why manufacturers still don't give a proper light or progress bar of DPF regens, notably on diesels. Every diesel I've ever had, I'd only notice by the smell of the car after stopping, the clicking of expanding metal, or it sounded a bit gruffer when driving, that a DPF had been underway, and then you wouldn't know if it had successfully finished properly anyway.