You're mixing two slightly different weapons here: the Kubotan and the ninja key chain
KUBOTAN -- the modernized version of the yawara stick -- was re-invented by a Japanese-born Karate master called Takayuki Kubota, thus the name Kubotan. It's about six inches long, made of plastic, weighs ca. 2 ounces, without any sharp edges.(*BB June 1982) Note: sticks and rods used to strengthen strikes are these days often generally called kubotans, especially outside the Japanese martial arts community (f.ie. police)
NINJA KEY CHAIN "is an aluminium bar similar to Kubotan except one end is filed to a point with two prongs jutting from the other end" (BB Feb 1985)
As you see, the ninja key chain looks, and is probably widely considered, more dangerous than the innocent looking Kubotan. That's why I think that there might be restrictions to carrying a ninja key chain that might not apply to the Kubotan.
I don't know if this helps, I hope it does.

(I'm not from USA.)
*BB : Black Belt Magazine
All the best,