As a noun:
* The stop sign was clearly visible.
* She gave him a sign that she was ready to leave.
* The doctor looked for signs of infection.
* The astrologer read the signs in the stars.
* The weather forecast was a sign of things to come.
* The new building was a sign of progress in the city.
As a verb:
* She signed the contract with a flourish.
* The band signed autographs for their fans.
* He signed up for the marathon.
* The artist signed their name on the painting.
* The dog signed its paw on the paper.
In idioms:
* He was giving off all the signs of being nervous.
* The fact that she didn't call was a bad sign.
* The company is showing signs of improvement.
* He's got the sign of the times on his side.