VKM meaning in General ?

A reporting mark is a code used to identify owners or lessees of rolling stock and other equipment used on certain rail transport networks. The code typically reflects the name or identifying number of the owner, lessee, or operator of the equipment.

In North America the mark, which consists of an alphabetic code of two to four letters, is stenciled on each piece of equipment, along with a one- to six-digit number. This information is used to uniquely identify every such rail car or locomotive, thus allowing it to be tracked by the railroad it is traveling over, which shares the information with other railroads and customers. In multinational registries, a code indicating the home country may also be included.