(a) No person shall act as a guard or lookout for any building premises or establishment used for gambling, prostitution, or any other form of vice or illegal act, or where intoxicating liquors are illegally kept, sold or purchased, or for any person soliciting, offering or engaging in prostitution, gambling or any other form of vice, or illegal act, or any prostitute, or any street or sidewalk.
(b) No person shall give any signal, intended to, or calculated to warn, or give warning of the approach of any peace officer to any person in or about such building or premises or places mentioned in the preceding subsection.
It is not necessary to show that the signal was given for any persons, it is sufficient if it is given to a person in the places mentioned.
People v. Hayes, CR A 1658.
but see:
People v. Mulder, CR A 2356.