The word Gouranga comes from the Hare Krishna religious movement. In Sanskrit it means "Golden One". Gauranga - also spelt Gouranga - is an alias of the movement's founding father, Shri Krishna Chaitanya Mahaprabhu, the "golden one", in veneration or because he was said to have had "golden" skin.
The word Gouranga and the phrase "Gouranga ! Be happy!" are of importance in part one and two of the Grand Theft Auto computer game series.
Stickers bearing the word Gouranga or stating Call out Gouranga and be happy! have been appearing on bridges over motorways and railways in the north of England over recent years. Similar stickers have also been appearing on public buildings, as well as the more recent surge of unsolicited (spam) emails bearing the same message. Stickers and fridge magnets with the phrase have also been handed out by 'monks' at recent music festivals throughout the UK, such as the Glastonbury and Donnington (Download) festivals.
More information can be found here: Desperately Seeking Gouranga (http://www.rlew.com/archives/00000117.htm)
Some people call this Hare Krishna spam because one meaning of Gouranga is Lord Caitanya Mahaprabhu