Sashimono

Sashimono (指物, 差物, 挿物) were small banners historically worn by soldiers in feudal Japan, for identification during battles. The sashimono poles were attached to the backs of the chest armor (dou or dō) by special fittings. Sashimono were worn by common soldiers, known as ashigaru, to elite samurai, and in special holders on the horses...
Found on http://en.wikipedia.org/wiki/Sashimono

Sashimono

Small banner affixed to the back of a suit of armor, for battlefield recognition purposes. Common in and after the 16th Century.
Found on http://www.samurai-archives.com/vocab.html

Sashimono

Small flag attached to the rear of an armour (Japan)
Found on https://www.royalarmouries.org/collections/glossary
No exact match found