Create 3D Block Markers on a Feature Line
Jowenn Lua walks through a neat trick to place 3D blocks on a Corridor Feature Line with Point Codes from a Code Set Style in Civil 3D.
From the Autodesk AKN Civil 3D Screencasts
See Jowenn Lua's AKN page
Corridor Code Set Style can automate some amazing stuff in Civil 3D. They sort of serve as an output Layer Manager for Corridors afterall.
This trick pretty much requires a separate Corridor for the Feature Line onto which you want to place regular blocks.
You certainly need a plan to name the blocks and appropriate Point Codes or it is easy to get lost and confused by the references.
You might also chose to employ the Corridor Station Point Labels workflow to generate point locations on the Corridor Feature Lines instead.
This method would allow you to swap on demand a set of 2D Plan symbols or 3D block symbols at the locations by Description Key Sets.