Question: So was Jax being a rat and the whole deal with Stahle a set up? ie. did the club know all along that Jax had something going on?
Chosen answer: Jax wasn't a rat. He knew he couldn't trust Stahl, which is why she got killed. The guys followed Jax and the others and beeped the horn, letting them know the job was done. I figure the club knows no government agent would actually be on their "side." More specifically, the club knew all along what was going on. In Jax's letter to Gemma, he explains how it was a club vote. This is meant to be everything Jax discussed with Stahl. He was simply sent to her alone because A) it needed to appear like he was actually ratting and B) Jax had the most to lose.
Chosen answer: It was the IRA's symbol (or their "tag"), an upside-down cross in a circle. It was done to frame them for the killings.
Bishop73