Long life 5" Invisible Ink Pen. Use an ultraviolet lamp to easily see the mark you've made on your valuables. This felt pen makes a broader, easier-to-see marks than other UV pens, good to add your personal secret markings on all types of surfaces. It has a yellow tint under the uv light. Water should work for cleaning it off, but it may need rubbing alcohol or a specialized stain remover needed to remove it completely.