As everywhere in Europe, the German laws protecting names connected to nobility stem from Salic Law. Nobility names are only inherited through marriage via the male line. Females of non-nobility can inherit a nobility name by marrying a man who can demonstrate nobility. If she remarries she cannot transfer a name signifying her connection to nobility to a husband who is of non-nobility or to their subsequent children. Non-nobility gentlemen do not gain the nobility name by marrying a lady of noble descent. Adoptions do not automatically allow one to carry the name of nobility. Such are the laws about nobility names. These guidelines were not always adhered to. Therefore, it is not always clear whether a connection to original noble families exists, especially since families according to new naming laws added a "von" to their name or obtained a nobility name through a mock marriage, adoption or purchase. This is also true for men who according to civil law now take over the nobility name of their wife and for women who obtained a nobility name through marriage and continue to use it after additional marriages as well was for children who carry the name of their mother (nobility name or acquired married name) without originating from a father of noble descent.
Source: http://www.adelsrecht.de/ - Namensrecht