I think Stripe started it long ago with "pk_" and "sk_" prefixes for public key and secret key.
Fun fact! They weren't always prefixed. And then after someone spent hours pouring over the logs in Splunk, that's when they had the idea of prefixing then.
that's actually a great reason / explanation. TY
I assume it's loose convention intended to identify the string as "Secret Key", as a hint to the humans who might be moving the data around, and maybe to make it easier to write precautionary code like "hey it looks like your commit has a secret key in it, are you sure you want to push it?"