The red necklace of the story is doubtless inspired by the ones worn by French fashionistas after the end of the “Reign of Terror”, in gruesome remembrance of the guillotine’s victims. The narrow red ribbon choker represented the severed neck and inset red stones were also sometimes added to represent beads of blood. These chokers were worn by both men and women, particularly at special Victim’s Balls(Bals des victimes)

Portrait of a young woman wearing one of these red necklaces. She looks as if she's also gone for another fashion trend of the time - lashings of white powder to create a "living corpse" appearance.
Madame Guillotine has put together a fascinating post about the "edgily morbid" fashions of the post-revolutionary period here:
http://madameguillotine.org.uk/2010/02/ ... rveilleuse