There have been many attempts over the years to categorise UFOs by their shape. Including it seems the US government.
Two photos from an alleged US Gov document dated April 1954, within the document on page 20 is a section depicting four UFO shapes : disc, cigar, cone and triangular. I find the triangular one very interesting as that shape has been really popular since the 1980s but was obviously flagged up by the US Government by the early 50s. Notice the light in each corner and the centre light which matches so many descriptions from around the world