Sound Cruiser by AmpliVox is the mountable version of the Half-Mile Hailer that is great for any vehicle: car, truck, police car, bus, etc!
It is a PA System that easily straps on the roof and projects crisp and clear sound. Plug in an external device or just greet those around you with the microphone (wireless mic is available).
Sound Cruiser YouTube Video
How to Set up the Sound Cruiser
YouTube Comedian Edbassmaster did a video called "Look at This" with the Sound Cruiser that now has over 800,000 views!!!
Other great items for a parade are:
--iPod Portable PA System
--Mity-Lite PA System
--Mity-Vox Personal PA System
Sound Cruiser Honors Veterans in Parade
Standing By America: AmpliVox Products Made in the USA