There seem to be a HTTP header[1] you could use. No icon though. And I'm not sure how much the restriction could be evaded by interactive Turing-complete CSS or

There seem to be a HTTP header[1] you could use. No icon though. And I'm not sure how much the restriction could be evaded by interactive Turing-complete CSS or similar features. [1] https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Co...