In most countries the idea that a cartoon piggy bank could incite a mob to violence would scarcely be plausible. Not so in India, where on Monday enraged Muslim protesters in the western state of Maharashtra attacked multiple offices of the prominent regional newspaper Lokmat.

The mobs were set off by a cartoon accompanying a story Sunday on Islamic State finances. It showed assorted currency symbols pouring into a piggy bank whose snout carried an image from the jihadist group’s flag—a white seal with black Arabic lettering...