The Archive of Esoteric Secrets
1-level Illusion (ritual)
You draw an arcane sigil on a surface you touch that can only be seen under certain circumstances. You can designate a particular event that must occur for the sigil to appear for 1 minute, before disappearing again. This can be as simple as "a humanoid comes within 20 feet of the sigil," to "the lever based puzzle must be correctly solved". When the sigil appears, it is unintelligable to most, and requires a successful DC 12 Intelligence (Arcana) check to decipher its meaning. The sigil can convey any message that you choose, as long as that message is no more than a word or short phrase. Truesight, or any other sense that reveals illusions can see the sigil without its specific conditions being met