I came across the above link on the Smithsonian website and found it so exciting to see how Man Ray was able to disguise his signature in his 1935 Space Writing photograph so well within the patterns of light swirls AND that it went undetected for so long. Here is an excerpt from the article written by Abby Callard.
"In 1935, the avant-garde photographer Man Ray opened his shutter, sat down in front of his camera and used a penlight to create a series of swirls and loops. Because of his movements with the penlight, his face was blurred in the resulting photograph. As a self-portrait—titled Space Writings—it seemed fairly abstract.
But now Ellen Carey, a photographer whose working method is similar to Man Ray’s, has discovered something that has been hidden in plain sight in Space Writings for the past 74 years: the artist’s signature, signed with the penlight amid the swirls and loops.
“I knew instantly when I saw it—it’s a very famous self-portrait—that his signature was in it,” says Carey, a photography professor at the University of Hartford. “I just got this flash of intuition.” Her intuition was to look at the penlight writing from Man Ray’s point of view—which is to say, the reverse of how it appears to anyone looking at the photograph. “I knew that if I held it up to a mirror, it would be there,” Carey says. She did, and it was."