A new view override feature called Reveal Constraints is part of the subscription only R2 release for Revit 2015. It is intended to make it easier to see constraints that have been applied to the model but may have been obscurred in some way. For example it is possible to use a padlock on a dimension string and then delete the string, ignoring the warning message and clicking OK to accept it but retain the constraint. Clicking the sneaky little dimension string with a padlock icon on the View Control Shortcut bar reduces the model to gray/halftone and displays constraints in a burgundy color, like below where I've locked a couple dimension between Levels.
Even constraints that are related to elements within a sketch are displayed but they are also gray or halftone. You can double-click to edit the element, if you have that feature enabled, or edit the element and then remove the constraint(s).
I've embedded the following video, which you'll find within Autodesk's help documentation.