Post flags. Flags of your home places, flags for your favourite social movements, silly flags, flags you made, flag remixes.
Please follow the guidelines laid out in the Community Covenant, available to read here: community-covenant.net/version/1/0 (with reporting section modified due to the structure of Sweet; please discreetly contact those who can help the most with a situation).
Also, remember to use content warnings for controversial flags. This is to not traumatise people, yes, but also to help people not run afoul of workplace, school, or national restrictions on the public viewing of certain kinds of content.