Visible crew/equipment: The reflector screen is reflected in Kelsi's eyeglasses, in many shots throughout the film.
Visible crew/equipment: After Gabriella and Troy convince everyone to stick with the musical, when Ms. Darbus asks everyone to line up she walks to stage left (viewer's right) and steps behind her white mark, on the otherwise clean stage floor.
Visible crew/equipment: When they are singing "A Night To Remember", with Ryan in the prop house with Sharpay in the bathroom (with the blue and pink background), there is a crew member reflected in the background colour.
Visible crew/equipment: When Jimmie and Donny are talking backstage of the senior year show, you can see a crewmember reflected on the pink picture.
Answer: I think that they are just props. The owner of those jerseys has no relevence to the plot.. They might just be randomly picked names.