What is an audio trade mark?

Think of Intel, they play it at the end of every TV and radio ad. That little 5 note theme is their audio trademark.

Think of the phone company... "I'm sorry, the number you have called is no longer in service." That's an audio personality and that particular voice is readily identifiable, you know it's the phone company.

Personalizing any audio prompt with your company name, corporate information, etc. is audio branding.