I think these secret message pens are super fun!
A few of my penpals and I each have a set so we can write secret messages to each other. Each pen contains invisible ink and the cap contains a black-light beam which illuminates the message. What a fun way to change up a letter and make it super fun!
See how the message appears once the blue light shines on it? So cool!
p.s. If you want a secret message writing set, you can get one here.