Superimposed “W” on terminal screen I don't know when it appeared, but I have a weird superimposed red "W" in iTerm2. What is it, and how do I get rid of it?

I'm running iTerm2 v 3.6.6 and macOS 10.15.
sounds like you are using an image as your background screen. Go to the iTerm2 menu and select Preferences. Under Preferences select Profiles and then go to the Window tab. See the image below. Check if you are using an image for your background. If you are click the enable box to turn it off.