I wanna say about folk habit , when people are not able to write letters, they put little stones tided with Pine needle in doors of beloved one. It was form of love letter.
Original it’s called [Koishi ni matsu 小石に松 ] which mean literately [ little stone in/and pine], but when you say it sound it like [ Koishiku matsu 恋しく待つ] which literally means [ I love you and I am waiting].
I think it’s incredibly romantic , more than all this stupid Valentines day XD
Also I wanna say this is not popular in Japan any more you can read about it in folk stories or legends , but I am sure if you give your Koishiku Matsu to someone they will be very,very confused .