Example:  http://math.stackexchange.com/questions/304000/x2y2-z21xy-prove-z-min-xyz-with-x-y-z-in-mathbbz

A "possible duplicate" warning prior to actual closing as duplicate seems to be a new feature.

If the question is closed you may simply see "closed as duplicate" at the same link.  I am talking about an unattributed notice prior to closure, currently there are 4 votes to close and the question is open.