[BobVA]

UPDATE:

I just asked my SO to check her 500, which isn't registered. The "About" page on that one says "Not Authorized for ebook Store".

So, that seems to be a relatively unmbigious way to tell if a Reader is registered to an account.

You can get to the "About" page from the "Settings" selection from the top-level on the Reader.

The only way I know to blow the registration data out of the Reader without deauthorizing via the Sony software (which deletes it from the current account and changes the authorization status on the "About" page) is to do a hard reset (much more involved than pressing the reset button).

If somebody HAD registered your Reader to an account, then done a hard reset, then failed to reauthorize and remove it from the account, I guess it could still be "registered", and this wouldn't show on the "About" screen. To get it into this state though, somebody would have to to know how to do a hard reset, which isn't documented in the manual.

I don't know what this would mean. You couldn't use it to read books on the old account, since it wouldn't have the registration information on the Reader necessary to read them.

If that circumstance existed and you then tried to register it to your new account I'm not sure if that would cause a problem or not (i.e. I don't know if Sony checks to see if the Reader still shows on someone else's account before letting you authorize it to yours) - I'll defer to PilotBob's info above however.

If the "About" page information isn't conclusive enough you could either try to register it as described by JSWolf, above, or perhaps Sony customer support could tell you if you read them the Device ID number (also on the "About" page).

Cheers,
Bob