Recently, on my facebook account, the LC-MS shared a link to an article in the Journal of Lutheran Mission with the following opening words:
On the Seventh Mark of the Church, as taught by Dr. Martin Luther
“Finally, “the holy Christian people are externally recognized by the holy possession of the sacred cross.”
Luther elaborates on the seventh sign by stating that Christians “must endure every misfortune and persecution… all kinds of evil.” In this way, they are conformed not by their own action and decision, but by the work of the Holy Spirit. They are punished not because they have done wrong, or because “they are adulterers, murderers, thieves or rogues, but because they want to have none but Christ, and no other God. Wherever you see or hear this you may know the Holy Christian Church is here.”
Below is a link to the excellent article. Well worth the time.
http://blogs.lcms.org/2014/suffering-persecution-and-martyrdom-as-a-mark-of-the-church-in-europe