What do the different onion icons in the address bar mean?

When browsing an Onion Service, Tor Browser displays different onion icons in the address bar indicating the security of the current webpage.

A green onion means:

• The Onion Service is served over HTTP, or HTTPS with a self-signed certificate.

A green onion with a lock means:

• The Onion Service is served over HTTPS with a CA-Issued certificate.

A grey onion with a red slash means:

• The Onion Service is served over HTTPS with a self-signed or CA-Issued certificate.
• The webpage contains subresources served over HTTP.