formal evening dress: vest or no?

[macwilkin]

MacLowlife, it's a Sergeant's sash. They're worn in the Commonwealth forces, are red, and denote Sergeants, Warrant Officers, etc. I've never worn one, so I'll leave it to someone else to give more detail.

Sashes were also worn by officers and NCO's of the US Army during the 19th century as a symbol of rank, and the officer's sash worn over the right shoulder:

http://howardlanham.tripod.com/link27.htm

T.