When I commented above about the trike rider that was hard to see from behind because he was so low, his trike was like the one in the photo below. But the one I was commenting on did not have panniers, instead he had a very low trailer with a large flat drybag on the trailer.
I suspect that the one with panniers was slightly more visible from behind. I took the photo above when the rider camped next to me at a campground in Iceland, I have not ridden it and know virtually nothing else about it other than I remember that the one in the photo I noticed had a Rohloff instead of derailleurs.