The Pitcairn Islands are a remote British colony in the South Pacific, famous for being the site where the mutineers from the HMS Bounty landed. The islands' population have always been very small (currently numbering around 50), yet, aside from the official anthem of God Save the Queen (which is not heard often on the islands), there have been, and continue to be, many unofficial anthems in use in the colony.
In Diana Jolliffe Belcher's 1871 book "The Mutineers of the Bounty and their Decendants in Pitcairn and Norfolk Island" it is reported that a local poem by Rev. G. H. Nobbs was set to the tune "Rousseau's Dream" and was considered by Pitcairners to be their anthem at the time. It is not known for how long this was considered as their anthem, however. Also, in 1856, several Pitcairners resettled on Norfolk Island as Pitcairn had become too small. The local anthem now in use on Norfolk Island (under Australian administration), Come Ye Blessed, is also referred to as the "Pitcairn Anthem", and more than likely was brought to the island by the Pitcairn settlers, suggesting that this anthem was in use on Pitcairn at that time. It is a hymn whose lyrics are directly quoted from the New Testament of the Bible (Matthew 25:34-36, 40).
Currently, the song "We From Pitcairn Island" (to the tune of the hymn "The Royal Telephone") is used as an unofficial anthem at gatherings and the like. Other songs, such as "The Goodbye Song" (written by Pitcairner Amelia Young) and the hymn "In The Sweet By and By" are considered unofficial "Pitcairn songs" at gatherings as well.
The above is an issued self-adhesive stamp (part of a set of 3) from Norfolk Island in 1994 with lyrics of "Come Ye Blessed", Norfolk's anthem which is also known as Pitcairn anthem.