Wow, just noticed sigs aren't even blocked when you ignore a user. That's a bigger hole in the system than subsequent quotes, if you ask me.
Since mobileread moderation relies on the ignore system so heavily, it'd be great to see an upgrade.
Edit: I've tried
this greasemonkey script in chrome, and it works well enough, excluding both the complete post, avatar and sig in all and excluding those posts that quote it (in full, not just the quoted portion). Just have to put
https://www.mobileread.com/forums/* in the @Include line and add the user names under var ignore_threads_from =. In chrome, you can save as *.user.js and then drag and drop the edited file into chrome to make it install.