the mark is visiable only under UV light,it's magic. Invisible UV Penwe are professional marker manufacturer1,this pen is made of totally new PP material and imported ink.2,pack: bulkCostomized package is acceptable,such as opp bag,blister card,colored box.3,Logo: silk print,transfer film,sticker4,Nib: bullet tip/chisel tip5,dry easily and nothing left on the paper6,the mark is visiable only ...