INVISIBLE MARKS SPOT RANSOM MONEY (Jul, 1937)
They’re not kidding when they call the dye “new”. Ultraviolet fluorescing dyes and paint had been developed by the late Robert Switzer and his brother Joseph in 1934 as described here
INVISIBLE MARKS SPOT RANSOM MONEY
Dipped in a new chemical solution and dried with a hot iron, ransom money is indelibly marked for identification. The preparation leaves no mark that a crook could detect, but the impregnated portion of the bill, which may be simply a strip along the edge, glows brilliantly when a bank teller holds the money under the invisible rays of an ultra-violet lamp.