I remember a security measure I've seen on a few sites in the past against phishing, but I don't know what it's called. When the user logs in, or just inputs their username, the site shows some kind of secret word / phrase / drawing. That word / phrase / drawing is something the user always sees, so it's proof for them that they're talking to the real site.

I know that American Express uses it, and I've seen a few other sites in the past use it too.

Does anyone know what it's called?