A shortcut is a representation of an existing node element placed on the same or a different diagram. 

Shortcuts facilitate reuse of elements, make it possible to display library classes on diagrams, and demonstrate relationships between the diagrams within the model. 

You can create a shortcut to an element of any other project in the current project groupsolution. You can create a shortcut to an inner class or interface of another classifier. It is also possible to add a shortcut to an element from project References, including binary (.dll, .exe) files. 

The small special symbol appears over a node to indicate a shortcut. It appears only if this node belongs to a different namespace or package. 

Select a shortcut on your diagram and choose Navigate To Element on the context menu to navigate to the source element in the Model View.