What do you call it when... someone's visual identity is unknown?

To contact us Click HERE
This query has been emailed into The Engine Room:

Is there a word which means that a person's visual identity is unknown? For example, the West End Whingers are often referred to as "anonymous" as people don't know what they look like. However, they are not anonymous as they really are called Phil and Andrew [the names given on the WEW website]. Is there a word for use in these circumstances?

Well, 'anonymous' comes from the Greek for 'nameless', whereas Phil and Andrew, I suppose, are faceless rather than nameless. However the OED defines faceless as "remote and impersonal", which isn't really what we're driving at. And whether it's true of the West End Whingers I wouldn't like to say!

Lots of other 'in-' or 'un-' words also spring to mind, such as 'incognito' or 'undisclosed', but none of them seem quite right. I imagine we're looking for another 'a-' word.

Any suggestions?