Angry Mob is a card in The Works.
The card's details are Mad and Townsfolk.
Angry mobs appear in the comic, but usually in the sepia tone of a flashback. The Angry Mob cards (there are four copies of the card) in The Works are not sepia-toned.
As mobs tend to grow, the instructions on the card are to pop (acquire and follow instructions on) an Angry Mob card.