It could mean "From Cologne":
see
this link at about.com
Geographical Surnames - Derived from the location of the homestead from which the first bearer and his family lived (Leon Meer - Leon from by the sea). Other geographical surnames in Germany are derived from the state, region, or village of the first bearer's origin, often reflecting a division in tribes and regions, i.e. low German, middle German and upper German. (Paul Cullen - Paul from Koeln/Cologne). Surnames preceded by "on" are ovften clues to geographical surnames, not necessarily a sign that an ancestor was of nobility as many mistakenly believe. (Jacob von Bremen - Jacob from Bremen)
see
this link at about.com
Geographical Surnames - Derived from the location of the homestead from which the first bearer and his family lived (Leon Meer - Leon from by the sea). Other geographical surnames in Germany are derived from the state, region, or village of the first bearer's origin, often reflecting a division in tribes and regions, i.e. low German, middle German and upper German. (Paul Cullen - Paul from Koeln/Cologne). Surnames preceded by "on" are ovften clues to geographical surnames, not necessarily a sign that an ancestor was of nobility as many mistakenly believe. (Jacob von Bremen - Jacob from Bremen)