In Civil 3D it appears you can only label one line at a time. This post will show a way to do label multiple lines using VBA. The first thing that needs to be done is to create a new vba project. The thing I learned while figuring out how to do this is using a selection set to select multiple objects. To create a selection set add it to the drawing's selection set collection. Once I'm done with it I need to delete it in order to be able to run the program again without getting an error that the selection set already has been created.
This is example just does lines, but the same concept could be done with polylines, feature lines, arcs, parcels and alignments.