This is one of those issues where I say we all band together and go full Karen as a community. It is so against the norms we've all agreed upon to live in this crowded city together we just cannot keep sliding downwards like this. I've been here 11 years and 100% of the "smoking a cig or other substance in a train car" incidents I've witnessed have all occurred within the last year and a half or so.

Say something in person if you deem it safe to do so (big judgement call here, do your best) or alert the conductor.