Sheppard's wristband
So I noticed he always wears a black wristband for some reason. I didn't really notice until he switched from wearing his Atlantis jacket to the SG-1 style black fatigues. I looked online, while I'm not the first to ask, I couldn't find an answer. In fact Flanigan seemed to avoid answering the question.
I looked up pics of the guy, he seems to always wear a bracelet or something, but otherwise no tattoos or anything they would feel needing to be covered up. Leaving it to be something that either the actor or writers felt like making Sheppard wear.