Well, I suppose that the gospel is not about conviction - conviction must proceed the gospel, but the gospel itself is the good news that we can be saved simply by faith, and that regeneration, faith, and sanctification were purchased by Christ on the cross.
Maybe two verses:
Problem - "No person shall ever be justified in His sight by obedience to the Law: for by the law is the knowledge of sin." (Rom 5:8) [front of shirt]
Solution - "By one sacrifice, He has perfected forever them that are sanctified." (Heb 10:14) [Back of shirt]
I would like to put this on a shirt:
Titus 3:3-7
3At one time we ourselves were also foolish, disobedient, deceived, serving divers lusts and pleasures, living in malice and envy, hateful, and hating one another.
4But after that the kindness and love of God our Saviour appeared toward man,
5 Not by acts of righteousness which we have done, but according to his mercy he saved us, by the washing of regeneration, and renewing of the Holy Ghost;
6Which he shed on us abundantly through Jesus Christ our Saviour;
7So that being justified by his grace, we should be made heirs according to the hope of eternal life."