URL Canary was created by James Stanley.
In early 2018 I was thinking about how to spread some decryption keys across several physical and virtual locations using Shamir's Secret Sharing Scheme so that even if one location is compromised, the keys are still secure.
But if an attacker were to slowly compromise several locations in turn, there might not be any indication that anything had gone wrong. That's how URL Canary was born. Alongside each piece of data, it's now possible to include a benign-looking paragraph about how to make use of the keys, including a helpful link to a web page promising more detailed instructions. The link to the web page is a URL Canary that, if accessed, will alert the owner of the keys, allowing defensive action to be taken before it's too late.