SIGNAL n.
A sign made for the purpose of giving notice to a person of some occurence, command, or danger; also, a sign, event, or watchword, which has been agreed upon as the occasion of concerted action. All obeyed The wonted signal and superior voice Of this great potentate. Milton.
SILVER CERTIFICATE n.
there has been deposited with it silver to a specified amount, payable to the bearer on demand. In the United States and its possessions, it is issued against the deposit of silver coin, and is not legal tender, but is receivable for customs, taxes, and all public dues.