Yes, they're prohibited. The reason? Well, they belong to a group of a whole bunch of things that are prohibited because someone got their knickers in a knot about sneaky silent and/or concealable weapons that might be used by imaginary ninjas. Basically, anything that's ever been used by a silent movie assassin is prohibited.
It's pretty silly, because many of those weapons can be made by anyone, and existing laws let you address that imaginary ninja, so prohibiting them serves little purpose.
