Simon (Peter) - Keys represent Peter as holder of the keys to the Kingdom of Heaven.
Andrew - (two symbols) An X-shaped cross is still called St. Andrews cross and is one of his Apostolic symbols. The other is two crossed fish because he was formerly a fisherman and was first Apostle active in bringing others to Jesus.
James (son of Zebedee) - His symbol is three shells, the sign of his pilgrimage by the sea.
John (known as Beloved Disciple) - It is said that an attempt was made on his life by giving him a chalice of poison from which God spared him. A chalice with a snake in it is his symbol.
Philip - His symbol is a basket, because of his part in the feeding of the five thousand.
Bartholomew (Nathanael) - He died as a martyr for his Lord. He was flayed alive with knives. His Apostolic symbol is three parallel knives.
Thomas (Didymas) - In India he suffered martyrdom and was killed by a lance. His symbol is a group of spears, stones, and arrows.
Matthew (Levi) - His symbol is three money bags reminding us he was a tax collector before Jesus called him.
James (son of Alphaeus) - He died as a martyr and his body was sawed in pieces. The saw is his Apostolic symbol.
Jude (Thaddaeus) - The chosen symbol for him was a ship because he was a missionary thought to be a fisherman.
Simon (The Zealot) - His symbol is a fish lying on a Bible, indicating he was a former fisherman who became a fisher of men.
Judas Iscariot - Betrayer of Jesus Christ - no symbol.
Mattias - Chosen by remaining eleven Apostles in order to have twelve again.
Information from NAS Bible, Special Study Aids, by Thomas Nelson, 1978, 1979.