The Writing on The Wall

Personally, I highly doubt that the writing was caused by paranormal activity. My best guess is there might be some chemical reaction going on in the buildings. Remember how the phantom dispersed gas in blue base in the first video in Season 2? What if something was released through the ventilation system to cause the wording to appear, assuming that the wording has always been there. If that is the case, than a device could be set on a timer to disperse the chemical at a certain time on a certain day.

Other than that, I see no physical reasoning of how that text just appear out of nowhere.