Whomever saw this unidentified flying object left a very detailed report on the sighting that lasted roughly ten minutes.

The UFO was viewed from an unknown site in Orrington, Maine, on Saturday, April 21st, and reported to UFO-Hunters.com.

The post said the the viewer used binoculars to view whatever it was, and made mention of how the craft didn't produce any sound.  The poster also made mention of previous sightings, so it sounds like this person may have witnessed UFOs in the past.

Here's the post:

Orrington, Maine (United States)

Sighted on Saturday 21. April 2018
Reported on Saturday 21. April 2018
Shape: Triangle | Duration: 00:10:00
Source: MUFON

(viewed through 10x50 binoculars for duration). first viewed exactly west from my position; travelling from south west > north east, losing sight just passed north due to building & tree obstruction, taking just under 10 minutes from first observed to last. moved very slowly, absolutely no sound, never going above 20 degrees above horizon. had 3 brilliant-white static lights in each of the 3 corners with one strobing red light centered on the underside hull. there was also a less-bright 4th light seemingly on the aft part of the fuselage, centered between (but higher) the two-rear lights. with binoculars, the fuselage against the background sky is clearly visible: a literal triangle, slightly longer than wide (ie, not equilateral), and relative to commercial aircraft, very dark. i've seen quite a few of these now, all following the same relative paths; sw>ne or ne>sw, in exactly the same two paths ie: directly east or west, which is so common i keep an eye out on either path. interestingly, the light-strobe pattern and colors were somewhat different with this: the red-strobe flashed more frequently than others in the past, and was exactly opposited by a strobing white light, seemingly from the aft-starboard white light. (they never went out of sync, compared to commercial aircraft). also compared to previous sightings, when at it's most southern position (front hull most visible), there were no red/green, port/sb winglet lights, which until now have always been visible from the front (not from the rear ever 100%). anyways, nothing special but i figured i'd report it for posterity. i would draw it but other than flashers and attitude indicator lights, it's the same basic vehicle people see daily. lastly, i must emphasize "no-sound." there were commercial aircraft much higher and further away that were distinctly audible, whereas this/these craft is/are not.