Earcon
An aural icon; an auditory brand symbol, United Airlines' use of "Rhapsody in Blue" as a brand expression would be one example.
Emotional Branding
Aims at customers' feelings through sensory experiences in the effort to brand-build.
Evangelist
An advocate for a brand, whether paid or unpaid.
Extension
A new service or product that leverages the brand equity of a related service or product.