When you first look at a work of art, ask the visitors what might be a good title for this piece. Anything goes! After a few have given their ideas, you can lead a discussion about each one, gathering what clues they saw to direct them towards their title. 

Then look at the label - is this a good title? 

Interesting discussions could also be why an artist chooses a title, should they be read first? Do they influence what you see?