We're all familiar with the typical post-sighting report involving helicopters or jets flying around the area. I'd like to discuss the unidentifiable strange phenomena (USP) preceding an event. I'm coming up with the USP to describe the noises (USN) and other things people report just before or during a sighting. Here is a shortlist to get started, I think it will help people recognize that something's possibly going to show up, so they can be prepared to document or at least witness it.

Stillness – not the least breath of wind, not a single leaf in motion

No stars visible on a cloudless night in part of the sky

An unusual noise

An unusual silence

Strange glow or color from horizon to horizon

Unusually black sky, few if any stars visible, moonlight blocked completely

Electrical static

Dysfunctional electronic aberrations

Uneasy feeling

Serene feeling

Animals behaving strangely – unusually quiet or agitated

Here is a link to an example, partway in the video, a girl in Florida experienced a USN coupled with unusual stillness