The shield is our official logo (it’s close, but different) - so no changes at this time, but we’ll see what  says as Big Sur gets closer to launch.
I have to admit that I wouldn’t have a better idea what to use instead, but my first thought when seeing the screenshots for the new Safari was that they used the Bitwarden icon
My safari extension icon is blue, but I would love for it to be monochrome. Is that a possibility?
I created an account to specifically put in a feature request for an option to change the color of the icon on the extension.