((This is an expanded version of the flyers left in-game.))
These flyers have appeared in the Rock Bottom, Upper gate, Upper bazaar, Upper stairs, Pissing Crone and Lower market.
"Attention, Spellcasters!
Worried that you might need to cast outside a warded area, or a job will take you outside the city? Decrease the danger to yourself and those around you! Purchase Abjurer's Nightshade! Lower market, every day.
[Fine print] *Unwarded casting will be safer, but still illegal."
((Every day from 2 to 2:40 PM US central time / -6 GMT))