I have read one historical joke, that during the Civil War Officer's shoulder bars were called "pumpkin rinds". Where are these mysterious shoulder bars from? I can find only shoulder boards or straps on the net. Is it some military slang? Obsolete form? Local variant? Or simply an error of the joke writer?
Shoulder bars are symbols of rank worn, as the name implies, on the shoulder.
Here's a page on ebay where someone is selling a WW2 variety: http://www.ebay.com/itm/WWII-US-NAVY-OFFICER-SHOULDER-BARS-/110564952372