Bitsig.io doesn't put arbitrary text into the blockchain. Given a string, if a Bitcoin address exists with sha256(string) as its private key, bitsig.io will publish the string, address, and first time the address was used. It also has tools for facilitating transactions to such addresses (which should never be used to store money). Hence stuff like this[0] from before bitsig.io existed.
0. https://bitsig.io/?addr=1AJ3vE2NNYW2Jzv3fLwyjKF1LYbZ65Ez64