In California there are only two CA State Penal Codes that refer to the legality of knives. That is not to say that each City can make its own laws governing knives. As far as CA State Law, there is nothing in the CA Penal Code that forbids a double-edged knife.
The two laws that I am refering to are 12020 PC (Which covers deadly weapons) and 653(k) PC which covers switchblades and balisongs.
PENAL CODE SECTION 12020
12020. (a) Any person in this state who does any of the following
is punishable by imprisonment in a county jail not exceeding one year
or in the state prison:
(1) Manufactures or causes to be manufactured, imports into the
state, keeps for sale, or offers or exposes for sale, or who gives,
lends, or possesses any cane gun or wallet gun, any undetectable
firearm, any firearm which is not immediately recognizable as a
firearm, any camouflaging firearm container, any ammunition which
contains or consists of any flechette dart, any bullet containing or
carrying an explosive agent, any ballistic knife, any multiburst
trigger activator, any nunchaku, any short-barreled shotgun, any
short-barreled rifle, any metal knuckles, any belt buckle knife, any
leaded cane, any zip gun, any shuriken, any unconventional pistol,
any lipstick case knife, any cane sword, any shobi-zue, any air gauge
knife, any writing pen knife, any metal military practice
handgrenade or metal replica handgrenade, or any instrument or weapon
of the kind commonly known as a blackjack, slungshot, billy,
sandclub, sap, or sandbag.
(2) Commencing January 1, 2000, manufactures or causes to be
manufactured, imports into the state, keeps for sale, or offers or
exposes for sale, or who gives, or lends, any large-capacity
magazine.
(3) Carries concealed upon his or her person any explosive
substance, other than fixed ammunition.
(4) Carries concealed upon his or her person any dirk or dagger.
Call me crazy, but nowhere in the code do I see mention of a double-edged knife. The closest thing is a Dirk or Dagger. If you look up the definition of dirk or dagger, not all double edged knives fall into that category. Also if a Dirk or Dagger is not concealed on your person, it is not illegal.
RJD