This is a Stickup

From 1914-1916 it was fashionable to have collars that were high in the back which complemented upswept hair held up with combs.  This was made possible by little items like this which were sewn inconspicously into the collars to hold them up.  Collar supports were not new, having been used for years earlier to support Edwardian lace collars, but these were the longest they would get.  See some examples below from the American Woman magazine of June 1915.