No one would take issue with fliers being hung around the castle, though they would be treated like any other random posting and are subject to any ne'er-do-wells who might be inclined to mess with them. Fliers advertising anything subversive of Thornean authorities will be torn down and the posters punished.

As there are no printers or copiers in Thorne, all fliers would need to be hand-written and illustrated. Hope you're artistically inclined, Zelda!