Bitcoin addresses are by convention expressed in Base58, which is a human readable binary-to-text encoding invented by Bitcoin. It is a bit like Base64, but obsessed with eliminating characters that look like one another in popular but stupid fonts like capital "I" and lower case ell "l".
This seems to be one of the earliest strategies used to encode messages.
The generated text is however rather obfuscated by the limitations of Base58.
The following transactions contain base58 encoded messages on addresses: