To indicate; to be a sign of.
To furnish (a traffic intersection) with a traffic signal.
To communicate with (someone) by means of a signal.
To give warning.
To notify or inform (someone, about something).
To caution or admonish (someone) against unwise or unacceptable behaviour.
To summon (someone) to or inform of a formal meeting or duty.
To advise or order to go or stay away.
To make (someone) aware of impending danger, evil, etc.