Pretty much every building in California has those warnings. Cars sold in California have a sticker on the driver window with that warning.
Another fun thing to do is to point the signs out to a California resident, who has probably long since completely edited them out of existence. It causes a "can't unsee!" reaction for about a week for certain people.
The graphite worked nicely on the lock.
To me, these labels are useless and dangerous for the same reason a lot of anti-drug education/propaganda is bad: it doesn't do anything to inform you about the relative level of danger. e.g. regardless of the affects of the drug itself, smoking a joint is _much_ less dangerous than injecting any substance with needles/syringes/etc which are not sterile.