As a noun:
* The traffic light signaled for us to stop.
* The signal was weak, so the radio reception was poor.
* The smoke from the fire was a signal for help.
* She gave me a signal to leave the room.
* The signal from the satellite was lost during the storm.
As a verb:
* The dog signaled its happiness by wagging its tail.
* The doctor signaled for the nurse to come in.
* The teacher signaled for the students to be quiet.
* The politician's speech signaled a shift in policy.
In a figurative sense:
* The low stock prices signaled a recession.
* Her silence signaled her disapproval.
* The author's use of symbolism signaled a deeper meaning.
These are just a few examples. The meaning of "signal" depends on the context in which it is used.