Philly needs a bit of holiday cheer. As far as I know, the operators pay out of their own pockets to do this. You can see it on some buses as well. philly.com has an article here: http://www.philly.com/philly/business/20151224_ThisChristmas_trolley_in_West_Philadelphia_gives_passengers_smiles_and_holiday_cheer.html
local railfans provide some visuals: