When reviewing commits, it would be nice to be able to 'tick' or 'checkmark' sections the reviewer reviewed and agreed with. This allows reviewers that follow the logic of the code logic throughout a change to see what they have already checked and what has not been checked yet.
The checkmark information should only be visible to the reviewer and only applies to a given patchset.
The "checkmark" could be literally be a check-mark next to sections or lines of code or could be color based: code sections are yellow until checked to green.