Charlies are usually very lightly marked brokens- they may have the nose spots (which look like a Charlie Chaplin mustache), ear color, and very little spotting. But- I have been reading up on them, and some Charlies have more color than others depending on the modifiers at work, so can look like a lightly marked broken.
A true Charlie comes only from a broken to broken breeding- a "False Charlie" is a very lightly marked broken coming from a solid to broken breeding. It may look like a charlie, but it cannot be one because it got one solid color gene from the solid parent.
A true Charlie will only have broken colored kits, so if you breed your alleged charlie (from a broken to broken breeding) and find a solid kit, it is a false charlie.