gouranga means golden limbs and refers to the last avartar of god who descended to earth 500 years ago.
This incarnation chaitanya mahaprabhu was golden in complection and so named golden limbs gauranga. he appeared in india and demonstrated how by chanting hare krishna mantra the soul is noticebly cleansed and perfection will be had through this process.
Hare krishna hare krishna krishna krishna hare hare hare rama hare rama rama rama hare hare.
on the bridges the monks put this up they say it means be happy but the name itself is happiness.