There have been found many ancient symbols used by the early Christians: a person with hands outstretched in prayer, a boat (symbol of the Church), an anchor (symbol of hope), two birds (symbol of peace), and so on.
Though there are dozens of these symbols or images (such as Christ the Good Shepherd) that have been used to express our Christian faith, one I have never seen anywhere is an image of Christ the Thief (perhaps it would show him wearing some kind of a mask, as a thief would be pictured today). But Jesus speak of himself in this way: "If the master of the house had known the hour when the thief was coming, he would not have let his house be broken into. In the same way, you must be prepared, for at an hour you do not expect, the Son of Man will come."
A thief is successful only because of the element of surprise. A thief will invade mostly at night when people are asleep & so not watching over their property. So the image of Jesus as a thief reminds us of the importance of staying awake. To be awake is to have a spiritual alertness, an awareness that the Lord who will come at the end of our life is with us now in our life. We need not be afraid if we are live in the light of faith and not in the darkness of sin. We light our 4 Advent wreath candles so that we may live in the light of the Lord.