This is the traditional bugle call known as Charge, which is mainly associated with the US Cavalry due its its frequent use during Western movies. The opposite call to recall the troops is the Recall. See the links at the left to download the sheet music or audio files. More bugle calls are listed in our article about the history and cultural impact of Bugle Calls
The image below is the first page of the sheet music, and here you can download the full sheet music for Charge (bugle call) in PDF format.