The following exert is an eye witness statement. Please read into it what you will. This has been reported to mufon who I am sure are investigating:
Walking on a parking lot i recognized a strange condense strip in the sky. the plane flew nw from vienna airport and was ascending, so the condense strip changed by height. i took a picture with my smartphone (nexus 5), because i loved the shape of the strip.
at home i uploaded the images taken that day to my server and had a closer look to the picture. there i saw the transparent ball next to the strip. it was not visible to me before when i looked up through the lens of my cam taking the snap. i am quite sure that i would have recognized it before taking the picture, if i could.