A bar code is integrated in the paper in the form of a watermark. The fields (6) which separate the information-conveying bars of the bar code from each other are formed as watermarks. The information-conveying bars can be formed as watermarks, but they do not have to. Their width results from the spacing of the separating fields (6). The separating fields (6) are more narrow than the information-conveying bars, as a result of which the total length of the bar code is kept short.