The banner reads 'Labour is death UK' - yet the stunt has not been explained.
In recent weeks a similar aircraft has been seen over Manchester and Liverpool, but an explanation for its presence was never given.
There has been speculation on social media that the message is political, while others think it could be a music promotion.
It was seen over areas including Leeds city centre, Chapel Allerton, Seacroft and Barwick-in-Elmet on Saturday morning.
It was later thought to have flown over York.