How to put your own message in the blockchain
It's pretty easy to put your own 20-character message into the blockchain. The following steps explain how.
1. Take your 20-character string and convert it to hex. E.g. in Python:
'//righto.com/bc'.encode('hex')
2. Convert the resulting hex string to an address. An easy way is online:
https://blockchain.info/q/hashtoaddress/your hex value yields 1AXJnNiDijKUnY9UJZkV5Ggdgh36aWDBYj.
3. Send bitcoins to that address and your message will show up in the blockchain when your transaction gets mined. Important: those bitcoins will be lost forever, so send a very small amount, like 10 cents. My test message can be seen at the end of blk00113 here.