This SS Sleeve Diamond would have been worn by an NCO in the SS-Totenkopfverbände. in the early years of the concentration camp system, before the skull was adopted on the collar tab (an NCO would have worn this with a K tab, a D tab, or something of that nature), the sleeve skull would have represented that the wearer was in the SS-TV.  This is a rare piece of insignia, the second in a set of two I acquired from an older collection.