Pure speculation: places where asymptomatic people wouldn’t mind being reminded they were depressed. (E.g. some of them might go to the gym to manage symptoms, but may not want to be reminded of the past in an environment linked with aspirational goals.) Maybe in pharmacies or the campus medical office, which they might associate with taking positive action for themselves towards self-care, and so feel a little more generous. Or department bulletin boards, or the university library, which might lead people to feel they’re contributing to a fellow peer’s work.
I see the tear-off papers mostly torn off when they’re hung in bathroom stalls on campus. (at sitting-down eye level <- experience limited to women's loos)
