Before the county of Corvis, there was the Wizard Corvus. Thirteen hundred years ago, a mad powerful wizard had an estate in the area that became the county of Corvis. Over his 800 year span, he created thousands of magikal items of various types and power level, some of which survive to this day.
Victorian Ladies used to use their decorative fans to communicate simple messages to their lovers while chaperones or husbands watched. These messages include "Yes", "No", "We've been discovered", "When can I meet you", etc. An Assassin's League of women could easily use this secret language to their advantage, sending messages to each other in hopes of reaching their target at a crowded ball.