SOX 2.8.0 and 2.8.3DEV both fail to load under Chrome on SE sites where you are not a member.
I don't know if this is intentional or not, but it seems like it should work regardless.
The settings icon ...
Here it is as a user script. I couldn't find a user style extension for my browser, but I'm already running Tampermonkey.
// @name StackExchange read-only mode
// @namespace https://...