During the Reformation period, many were asking about how to recognize the true Church. Martin Luther described seven marks of the Church; Holy Word of God, the Sacrament of Holy Baptism, the Sacrament of Holy Communion, Holy Absolution, Holy Ministry, Holy Prayer, and the Holy Cross. Where those are present, true faith can be found. For a fuller understanding of Luther's Seven Marks of the church, see Luther's Works, Volume 41, "On the Councils and the Church," especially pp 143-166.
In 2009, pastors and laity formed The Seven Marks Society (SMS). The original purpose of the SMS was to develop orthodox resources for individuals and congregations to use with reasonable confidence to transmit the orthodox faith. At the same time, there has been a desire to encourage prayer among lay members of Lutheran congregations in North America.
Quotations are from Luther's Works, Volume 41 (LW)
Page references are from CONCORDIA The Lutheran Confessions Concordia
Publishing House Second Addition, Copyright 2005, 2006 (CLC)