UV inks have been getting a lot of attention lately and even more so when this brilliant Harry Potter-themed ink was made viral. At first, it only appears to be a set of footprints akin to that found on the Marauders' Map (what Harry uses to get away from a lot of troubles) but when exposed to UV light, the words "I solemnly swear that I am up to no good" appears below.

This is one cool ink that we'd like to have as well!