This is the traditional bugle call known as Recall, which is used to order troops to return and regroup. It is associated with the US Cavalry since it can be heard on some Western movies to recall the forces after a Charge. 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 Recall (bugle call) in PDF format.