The noun 'ambulance' is a common noun, a word for any ambulance anywhere.
A proper noun is the name of a specific person, place, or thing; for example:
- Braun Custom Ambulance, Braun Industries, Inc., Van Wert, OH
- Quaker Valley Ambulance Authority, Moon Township, PA
- Medic-West Ambulance (service), North Las Vegas, NV
- Air Ambulance Worldwide, Inc, Clearwater, FL