Some cities have their own laws regarding graffiti. The following is the City Of Ventura,CA. Code.
Furnishing to minors Sec. 10.250.040
It shall be unlawful for any person, other than a responsible adult, to sell, exchange, give, or loan in any way furnish to any minor any graffiti implement.
Sign Sec. 10.250.090
Any person engaged in the retail sale of graffiti implements shall display at the location of retail sale a sign, in letters at least three-eights of an inch high, clearly visible and legible to employees and customers which states as follows:
"IT IS UNLAWFUL FOR ANY PERSON TO SELL OR GIVE TO ANY INDIVIDUAL UNDER THE AGE OF EIGHTEEN YEARS, WHO IS NOT ACCOMPANIED BY A RESPONSIBLE ADULT, ANY AEROSOL CONTAINER OF PAINT OR OTHER SUBSTANCE, PAINT STICKS OR INDELIBLE MARKERS"
A responsible adult shall mean a parent or legal guardian or school teacher of an individual under the age of 18 years.
Graffiti implement shall mean an aerosol container, an indelible marker, a paint stick, or a glass etching tool.
For more info on your city's graffiti codes check your city website or contact your city clerk.