Don't bank on that method because you won't be the only one who knows or understands how to use an ultraviolet ray to decode stuff on papers. My idea of masking secret words/stuff is to make them look as ordinary as possible. It's the same method local men in Africa who carry huge cash around use. They appear unkempt and unassuming when ferrying cash across in a way that even robbers are likely to miss them on the road.