Bitcoin’s block chain is a decentralized database which main purpose is to secure and hold all Bitcoin transactions. It can be used to store other data too. For example, lovers might want to “scratch” their name letters to the block chain where they will remain forever.
The authors of this site have developed a web service that enables users to read and write Bitcoin blockchain messages. It is named CryptoGraffiti Decoder and it decodes secret messages saved into block chain. The service is free and even allows users to compose their own bitcoin block chain messages that can be easily stored in the block chain. To send an arbitrary message to the Bitcoin’s block chain, one should use http://cryptograffiti.info and import the generated addesses to their wallet in the same order the service has generated them.