never thought i'd see a yuri story written about The Gay Ear
During my days, it was akai hito(the red string I think?)
But I think it only applies to hetero couples ( though if I'm not mistaken, there's a yuri manga here also talks about the red string, and in an ambiguous way, that says the red string connects you to your destined one ( whether it be hetero or same sex couple)
Then there's this pinky promise...
And then there's this wearing your ring on certain finger points out your sexuality in a vague manner
The ear one is definitely the first I've heard on this manga xD