Knife with interesting markings - Ebay

[David]

The 3rd Armored Cavalry Regiment was formed in 1846 and probably did serve in the Philippines, though the Wiki article on them has a hole in it for that period. You will notice though that their insignia does indeed include a trumpet and the number 3.
They were nicknamed "The Brave Rifles" and their motto is "Blood and Steel".
http://en.wikipedia.org/wiki/3d_Armored_Cavalry_Regiment_(United_States)

[David]

This is their current insignia, but i am certain that the design would have been different back then, though it still probably maintained the same elements like the bugle.

[David]

Also the symbol on the reverse side from the triangle and sun looks like a cavalry flag, does it not?

[Rick]

Originally Posted by David

Also the symbol on the reverse side from the triangle and sun looks like a cavalry flag, does it not?

Very much like a Guidon, David .
The trumpet insignia on the scabbard looks old fashioned; perhaps a holdover from the Civil War ?