tl;dr: Search Gmail for “
is:spam -label:^os” to find messages that you manually marked as spam (as opposed to ones that Gmail automatically marked for you). Mihai Parparita
Great insight into Gmail’s hidden labels! Many have been uncovered already over the years, like Superstars and Smart Labels, and other have clear equivalents in the user interface. Besides the more fine-grained classification of spam messages, another system label could prove useful,
^p_esnotif, which marks notifications from Google+. You can search for all your Google+ notifications with the command
l:^p_esnotif or create a filter to file them automatically under a label, archive them or whatever else you might want to do.