I don't see anything in the city code, but the county code has some restrictions. It looks like anything with more than 3" blade is a "dangerous weapon."
3.16.010 Definitions.
For the purposes of this chapter, certain terms, phrases and words shall be construed as follows:
(a) "Switch-Blade Knives" shall include, but shall not necessarily be limited to the following: all spring-blade knives, switch blade knives, snap-blade knives, or other similar knives of which any blade thereof, regardless of length, is released automatically by a spring mechanism or other mechanical device, or is released by any type of mechanism whatsoever.
(b) "Dangerous Weapon" shall include, but shall not necessarily be limited to the following: any knife with a blade three inches (3") or more in length, any ice pick, awl, dirk, dagger, stiletto, or similar sharp stabbing tool, any straight-edged razor, razor blade fitted to a handle, razor with an unguarded blade, or any cutting, stabbing or bludgeoning weapon or device intended to be used as a club or capable of inflicting grievous bodily harm.
(c) "Public Place" shall include but shall not necessarily be limited to the following: any public street, way, sidewalk, alley, public park, beach, recreational area, school, public building or place of public resort, any place where an athletic event, dance or other such gathering to which the public or a number thereof are admitted, and any place where alcoholic beverages are sold.
(Prior code § 3140; Ord. 1196, 12/11/56)
3.16.020 Sale or possession of switch-blade knives prohibited.
No person shall sell, offer for sale, expose for sale, keep, carry, possess, loan, transfer, or give to any other person any switch-blade knife.
(Prior code § 3141; Ord. 1196, 12/11/56)
3.16.030 Possession of dangerous weapons in public places prohibited.
It shall be unlawful for any person having in his possession or immediate physical control, whether the same be concealed or visible, any dangerous weapon, to loaf or loiter upon any public place, or to wander about from place to place with no lawful business thereby to perform, or to hide, lurk or loiter upon or about the premises of another.
(Prior code § 3142; Ord. 1196, 12/11/56)
3.16.040 Possession prohibited continued--Public disorders.
It shall be unlawful for any person having within his possession or immediate physical control, whether the same be concealed or visible, any dangerous weapon, to engage in any fight or to participate in any riot, uprising or other type of disorderly conduct upon the premises of another or upon any public place.
(Prior code § 3143; Ord. 1196, 12/11/56)
3.16.050 Exception.
The provisions of sections 3.16.030 and 3.16.040 shall not be deemed to prohibit the possession or control of ordinary tools or equipment carried in good faith for the purpose of honest work, trade or business, or for use in a legitimate sport or recreation.
Nothing in this chapter shall prohibit police officers, special police officers, peace officers, or other law enforcement officers from carrying any wooden club, baton, or any equipment authorized by the properly constituted authorities for the enforcement of law in San Mateo County.
(Prior code § 3144; Ord. 1196, 12/11/56)