Jayne has quite a collection of T-shirts, and one of the more famous is his Blue Sun shirt. He only wears it in two episodes, though. It looks like Jayne has cut the sleeves and collar out of the shirt to make it more comfy.
More pictures after the break...
The above and this one are both from Ariel.
Nice view of his tattoo, right?
This one is when we first see this shirt in Bushwhacked.
My Photobucket album for Jayne.
Serenifly Costumes site for Jayne.