Set private labels or bookmarks

This comes from feedback from the OS community:

• Support “private labels” for issues. Users should be able to add private labels to any issue, even if it’s a project they don’t maintain. They should then be able to use them for querying/filtering.

This is an interesting idea, but I'm not sure how it would work out. In general it's preferable to share such information (i.e. add more labels).