In Revit Structure 2012, if you go to Manage > Structural Settings > Analytical Model Settings and turn on the option to Differentiate ends of linear analytical elements, you'll find that you can now see which end of the member is the Start and which is the End:
If you are working with a model that you have upgraded from a previous version of Revit, when you turn on this option in Structural Settings, it might look like the new functionality is not working:
The reason for this is that by default in upgraded files, the display of the Start and End Segments is set to the same color as the rest of the Analytical Model. To adjust this, you can do the following:
Open Manage > Object Styles and switch to the Analytical Model Objects tab.
Expand the Analytical Beam, Brace, and Column categories. You'll see that the End Segment and Start Segment categories are the same color as the rest of the Analytical Model.
Adjust the colors as desired. The following screenshot shows the default 2012 template settings:
Another option is to use Manage > Transfer Project Standards and transfer the Object Styles category from the default 2012 template to your upgraded project.