C stands for "Catholics".

4 stands for the word "for".

t stands for Truth.  Jesus is the Truth.  "I am the way, the truth, and the life" (John 14:16).

The letter t is in the shape of the cross.  If Jesus did not die on the cross for us, we would not have gained eternal life.  The reason our logo needed to have a cross is because of its significance throughout history.  On example is Emperor Constantine's vision.  He had a vision and saw a Cross which emblazoned on the horizon with the words "In Hoc Signo Crucis Vinces" meaning that "In This Sign (The Cross) You Shall Conquer".  The Emperor Constantine immediately placed a cross on the shields of everyone in his army.  Even though his army was fiercely outnumbered by the contending emperor Maxentius, Constantine swept the enemy into the Tiber River, and entered victoriously into Rome!  Because of this incident, the trail for the Edict of Milan was issued and ended the persecutions against Catholics, and gave them the legal right to worship publicly.

Notice that the letter C strives to embrace the letter t...as Catholics, we should embrace the cross (i.e. the sufferings in life) as Jesus Christ, manifested as Man, suffered crucifixion and died on the cross for us.  Like Constantine, we shall conquer if we embrace the cross.  We should also strive to embrace the Truth, which is Jesus.  But in reality, there will be always obstacles in our pursuit of embracing the cross and the Truth.  The number 4 between the letters C and t reminds us of this fact.

If you look at the whole logo, you will notice that the C4T logo resembles a fish .  This is an early symbol for Christ.  Also, the use of fish is significant in many parts of the bible, such as: "Come after Me, and I will make you fishers of men" (Mark 1:17).  St. Peter as well as some other apostles were also fishermen.