Real Dictionary

signal
an arrangement of two or more things in a successive order [...]
any device, such as a microphone or electric motor, that converts one form of energy into another [...]
any of a group of compounds consisting of two or more amino acids linked by chemical bonding between their respective carboxyl and amino groups [...]
any sign, gesture, token, etc, that serves to communicate information [...]
the act or fact of changing or being changed [...]
the state or quality of being intense [...]
the transfer by a bacteriophage of genetic material from one bacterium to another [...]
You use signal to describe a success or failure when you are emphasizing the fact that it has occurred and are indicating that the consequences are significant.
countable noun: A signal is a gesture, sound, or action which is intended to give a particular message to the person who sees or hears it.
countable noun: A signal is a piece of equipment beside a railway, which indicates to train drivers whether they should stop the train or not.
countable noun: A signal is a series of radio waves, light waves, or changes in electrical current which may carry information.
countable noun: If an event or action is a signal of something, it suggests that this thing exists or is going to happen.
verb: If someone or something signals an event, they suggest that the event is happening or likely to happen.
verb: If you signal to someone, you make a gesture or sound in order to send them a particular message.