the first year I saw them I thought they MUST have been leftover from a mixer I'd missed. NOPE.

There's a lot of problems with asking people to self-identify as allies (especially when the # of ribbons is FAR LESS than the # of attendees). Mostly, there's no guarantee those people are "safe" and it draws attention to how sparse they are - is everyone else willfully unsafe? It also basically identifies them as most likely not queer. All of this has been better said by other people, but I fundamentally agree.