I guess the sign is not in keeping with rabbinic thinking. According to Rashi and the Midrash, the great virtue of the eagle is that it carries the young on its back in order to shield them from men’s arrows.
Later I was helping out at the Chabad house when I mentioned Lewis to Mrs. Freida Brackman. She responded that she taught Lewis’ grandchildren. I response was: “so you know David Gresham.” Lewis late in life, married an American divorcee named Joy Davidman. She was an ex-Communist, who had converted to Christianity. Joy was originally from a secular Jewish family. Joy had two children, David and Douglas Gresham. (Lewis actually dedicated the Horse and His Boy to the two of them.) Joy died of cancer leaving the two children with Lewis. As a teenager David Gresham became an Orthodox Jew. Interestingly enough, Lewis actually paid for David’s Yeshiva education. According to Mrs. Brackman, David and his wife are extremely eccentric. I would certainly love to meet them. Judging from the fact that there is little information available about David on the web, I assume that he is a very private person, who likes to avoid the public spotlight.