Solution

The latin title hints towards the previous task Sidereum Nox. By taking the coin artefact with you to the different posters, you can see that there is a circle shaped splotch of the same size as the coin. By placing the coin in the center and aligning the logo on the coin to the logo on the poster, you get letters from each poster. The letters are ls, a, t, de. By taking the letter groups in numbered order suggested by the posters and doing some light shuffling of the letters, you get slated.