Looking at your avatar, the following excerpt from the 1861 US Army Regulations may be of interest:
299. The usual badge of military mourning is a piece of black crape around the left arm, above the elbow, and also upon the sword-hilt; and will be worn when in full or in undress.
300. As family mourning, crape will be worn by officers (when in uniform) only around the left arm.
I expect CS regulations were similar, but don't have a copy to verify.