Jayne Cobb was a man who thought of his body as a canvas, and this was something his multiple tattoos would attest to. So it came as no surprise when he mentioned that he was going out to get another one. When asked about the nature of the tattoo, he remained evasive, refusing to tell its location, and only saying that it was a representation of what saved his life. The crew assumed it was simply a tattoo of Vera, or another one of his guns, and forgot the matter.
This is why it came as such a shock to Simon two weeks later, when Jayne had taken a bullet in his shoulder and was doped up and ready to go under his knife to have it removed. Simon removed his shirt to begin, when he saw Jayne's mysterious new tattoo for the first time. Upon his chest, directly over his heart, was an angel. But this angel was not a muscled man with blonde hair and a flaming sword. This angel was small, petite, with dark hair and deep brown pools for eyes. This angel was a strong looking female with a beautiful face. But what moved Simon the most was her feet, for upon the angel's tiny feet were ballet shoes.