In our times the Church and her credibility are the most often rejected elements of Christianity by ordinary European citizens. The Church’s credibility is questionable also for many Christians, who find Ecclesia split into two: how she should be and how she really is. Because of that theology needs objective, scientific research on the Church’s credibility. This is the task of Fundamental Ecclessiology which uses – among others – a method called signs of the Church’s credibility. These signs could be described as two-dimension elements which consist the Church and direct to her supernatural, Divine origins. In this article one can find a short presentation of about fifty such signs. All of them are fulfilled in the real Church in a different level (no-one in 100%). They are also recognized in a different intensity which depends on many subjective and out-subjective factors.