It turned out to be the Goodyear blimp.
It was dusk and you could not actually see the main body of the airship at all. Only the brightly lit advertising panel that looked like a colorful energy field in motion kind of like science fiction renditions show underneath a flying saucer keeping it aloft relatively still in the sky.
A different time in the 1990's I was traveling from north Florida toward South Florida, out in the middle of nowhere between Ocala and Orlando late at night.
Didn't see anything flying, but at high altitude there clearly appeared quite quickly in a clear sky a geometric grid of contrails. Perfect square crosshatch pattern which lingered for almost a half hour as the lines in the sky gradually diffused.
Traveling at speed I was able to estimate the sides of each square were 25 to 50 miles long, and I had to think the overhead pattern extended from coast-to-coast across the state from ocean to gulf. I was about in the midpoint between the coasts. Easily extended north-to-south equally as far, and I wouldn't have been surprised if it covered hundreds of miles of longitude beyond what my direct observation could estimate.
There was no physical way a single known aircraft had simultaneously laid down these trails, they were all the same thickness and dissipated at the same rate, and the whole pattern freshly appeared at once.
None of us had any clue what it was.
The newspaper the next day said it was from a failed rocket launch at nearby launch facility.
For a similar example, see the 2009 "Norwegian spiral anomaly", from a failed Bulava missile test. Which some also called a UFO.
If by "UFO" you mean something that can only have been caused by an extraterrestrial craft? No.