Biblically speaking, Signs are miraculous events or physical manifestations performed directly by God or by God through one of His humble, available servants, helping to prove God's Sovereignty. (my definition)
After performing a word search on of Signs, the following is how I found the word to be used.

In Genesis 1:14 there is the use of signs that refers to the mark of the seasons.
"And God said, "Let there be lights in the expanse of the sky to separate the day from the night, and let them serve as signs to mark seasons and days and years,"

Most of the book of Exodus uses signs as proof of God's miracles by using Moses to force pharoh to let His people go.

In 1 Sam 10:7, the word signs is used as proof of fulfilled prophecy.
"Then Samuel took a flask of oil and poured it on Saul's head and kissed him, saying, "Has not the LORD anointed you leader over his inheritance?  When you leave me today, you will meet two men near Rachel's tomb, at Zelzah on the border of Benjamin. They will say to you, 'The donkeys you set out to look for have been found. And now your father has stopped thinking about them and is worried about you. He is asking, "What shall I do about my son?" '  "Then you will go on from there until you reach the great tree of Tabor. Three men going up to God at Bethel will meet you there. One will be carrying three young goats, another three loaves of bread, and another a skin of wine.  They will greet you and offer you two loaves of bread, which you will accept from them.  "After that you will go to Gibeah of God, where there is a Philistine outpost. As you approach the town, you will meet a procession of prophets coming down from the high place with lyres, tambourines, flutes and harps being played before them, and they will be prophesying.  The Spirit of the LORD will come upon you in power, and you will prophesy with them; and you will be changed into a different person.  Once these signs are fulfilled, do whatever your hand finds to do, for God is with you."

One can find literal signs/banners to signify occupation of the land in Psalms 74:4.
"Your foes roared in the place where you met with us; they set up their standards as signs."

There is a lack of miraculous signs concerning deliverance from enemies just five verses later in Psalms 74:9.
 "We are given no miraculous signs; no prophets are left, and none of us knows how long this will be."

Isaiah 8:18 labels the people of Israel as a sign. 
"Here am I, and the children the LORD has given me. We are signs and symbols in Israel from the LORD Almighty, who dwells on Mount Zion."  

So we have signs as a group of people that God miraculously works through.  However, He works through individuals as well and calls them signs, like Mary and the baby Jesus in Isaiah 7:14.  "Therefore the Lord himself will give you a sign: The virgin will be with child and will give birth to a son, and will call him Immanuel."  

Signs were requested of and expected of God in prayer by Peter, John, and the believers in Acts 4:23-30.  "On their release, Peter and John went back to their own people and reported all that the chief priests and elders had said to them.  When they heard this, they raised their voices together in prayer to God. "Sovereign Lord," they said, "you made the heaven and the earth and the sea, and everything in them.  You spoke by the Holy Spirit through the mouth of your servant, our father David: " 'Why do the nations rage and the peoples plot in vain?  The kings of the earth take their stand and the rulers gather together against the Lord and against his Anointed One. '  Indeed Herod and Pontius Pilate met together with the Gentiles and the people of Israel in this city to conspire against your holy servant Jesus, whom you anointed.  They did what your power and will had decided beforehand should happen.  Now, Lord, consider their threats and enable your servants to speak your word with great boldness.  Stretch out your hand to heal and perform miraculous signs and wonders through the name of your holy servant Jesus."  

The apostles are listed in Acts 5:12 as involved in delivering miraculous signs. 
"The apostles performed many miraculous signs and wonders among the people. And all the believers used to meet together in Solomon's Colonnade."  

Stephen, (Acts 6:8)  Phillip (Acts 8:6), plus, Paul and Barnabas (Acts 14:3) displayed the power of God in their lives through miraculous signs.  So, individuals got in on the "act" (get it, most of these examples came from the book of Acts-hahaha). 
"Now Stephen, a man full of God's grace and power, did great wonders and miraculous signs among the people."
"When the crowds heard Philip and saw the miraculous signs he did, they all paid close attention to what he said."
"So Paul and Barnabas spent considerable time there, speaking boldly for the Lord, who confirmed the message of his grace by enabling them to do miraculous signs and wonders."

Signs can be a way to determine the times we live in.  They can point where we have come from, where we are, and most importantly where we are headed (Matthew 16:3).
"...and in the morning, 'Today it will be stormy, for the sky is red and overcast.' You know how to interpret the appearance of the sky, but you cannot interpret the signs of the times.

Signs are also proofs that believers of the faith are true believers (Mark 16:17).
"And these signs will accompany those who believe: In my name they will drive out demons; they will speak in new tongues;"  

Signs in Luke 1:22 simply meant hand motions or some kind of communication that Zechariah used because Gabriel pronounced him mute until John was born.
"When he came out, he could not speak to them. They realized he had seen a vision in the temple, for he kept making signs to them but remained unable to speak."

Astronomical events, like the ones found in Luke 21:25 are another use of the word signs.
"There will be signs in the sun, moon and stars. On the earth, nations will be in anguish and perplexity at the roaring and tossing of the sea."

You can misuse signs.  Signs can be used as a "crutch" (John 4:48).
"Unless you people see miraculous signs and wonders," Jesus told him, "you will never believe."

There are and will be conterfeit signs according to 2 Thessalonians 2:9.
"The coming of the lawless one will be in accordance with the work of Satan displayed in all kinds of counterfeit miracles, signs and wonders,"

Signs can also be found within heaven and I mean the spiritual domain where angels can be seen and considered signs for those who see them (Revelation 15:1).
 "I saw in heaven another great and marvelous sign: seven angels with the seven last plagues--last, because with them God's wrath is completed."

Signs can be mysterious symbols that require research to reveal their identity (Revelation12:3)
"Then another sign appeared in heaven: an enormous red dragon with seven heads and ten horns and seven crowns on his heads."

So, the next time you speak of a sign to anyone, make sure you are clear, the usage is varied greatly.