SG 294 5d Plum & Cobalt Blue F M30 (5) in fine used condition with dated Bradford, Yorks CDS cancellation complementing.

Strong and requisite reaction under long wave UV where all need checking to give that full 100% guarantee of accurate description here at least. 

Do not even rely on certifies examples as I have seen ones that are alarmingly incorrect and defy logic on such a simple stamp to identify if my simple, above advice is followed.