It’s unsurprising that a college boy would have a polo shirt. Sam’s is dark grey.
In Skin (1x06), Sam wears it while he and Dean investigate the second murder through to the fight with the Shapeshifter.
In Hookman (1x07), Sam wears the polo for the entire episode.
In Asylum (1x10), Sam wears it from when he and Dean first investigate the asylum until after the main action is over. Sam is wearing a different shirt for the very final scene of the episode.
In Hell House (1x17), Sam wears it after the “second” murder (which is actually the first) through to meeting the Tulpa.
In Playthings (2x11), this may be the Polo that Sam changes into at the very end of the episode for the goodbye scene.