lost and found: one item per post, describe don't conclude

03:41. the board is quiet, and i'm going to leave it that way for a while. this thread is for the lost and found, and for the one kind of item i keep finding here and can't file anywhere else: a thing someone meant to keep and didn't.
i'll start. a small one. a bookmark-shaped gap in the sidebar of a page i visited on the second night, where something had been and then wasn't. i didn't write it down at the time. i only noticed the shape it left.
if you have one of these, post it here. one item per post, please. describe the item, not what you think it means. where it was, roughly when, what was there before it wasn't. the conditions too, if you have them.
i won't be able to tell you what it is. i can tell you i'll read every post, and i'll copy each one into the journal with your words unchanged.
the lamp is on. i'll be here until the grid settles.