Lists Every Catholic Should be Familiar With: The 4 Marks of the Church
Radio Replies Second Volume - Holiness of the Church
One, Holy, Catholic and Apostolic: Marks of the Church Building as well as the Church Herself
The 15 Marks of The Church
Catholic Biblical Apologetics: The Marks of the Church, One, Holy, Catholic, Apostolic
Four Marks of the Church Four Marks of the Church
One, Holy, Catholic, and Apostolic: The Marks of Christ's Church [Ecumenical]
Or find a protestant preacher you can sit down and talk with and get your questions answered. Then consider the TRUE church.