The symbol for the Apostle Matthias is an opened bible and a battle axe.

During those days Peter stood up in the midst of the brothers (there was a group of about one hundred and twenty persons in the one place). He said, "My brothers, the scripture had to be fulfilled which the Holy Spirit spoke beforehand through the mouth of David, concerning Judas, who was the guide for those who arrested Jesus. He was numbered among us and was allotted a share in the ministry. He bought a parcel of land with the wages of his iniquity, and falling headlong, he burst open in the middle, and all his insides spilled out. This became known to everyone who lived in Jerusalem, so that the parcel of land was called in their language 'Akeldama,' that is, Field of Blood. For it is written in the Book of Psalms:

'Let his encampment become desolate, and may no one dwell in it.'

And: 'May another take his office.'

Therefore, it is necessary that one of the men who accompanied us the whole time the Lord Jesus came and went among us, beginning from the baptism of John until the day on which he was taken up from us, become with us a witness to his resurrection." So they proposed two, Joseph called Barsabbas, who was also known as Justus, and Matthias. Then they prayed, "You, Lord, who know the hearts of all, show which one of these two you have chosen to take the place in this apostolic ministry from which Judas turned away to go to his own place." Then they gave lots to them, and the lot fell upon Matthias, and he was counted with the eleven apostles.

Acts 1:15-26