I would lose it

It’s nuanced right? I mean- if your room mate/live in partner is leaving festering food around or your living room looks like a garbage dump that’s going to be pretty clear they need to clean up after themselves- but most people don’t want to live with somewhere where they can’t set their keys or their jacket or their laundry or whatever down for a little bit if they are running to do something else or what not and it will be gone later. So if my partner isn’t a slob and she leaves her jacket on the couch or her sock somewhere- I’m going to figure that’s probably her business. If I move it and she knew where it was or left it there with intent- maybe she’s looking later and is like: “where’s my sock? I knew it was here…” If it’s there maybe some hours later or the next day then I might ask about it like “did you lose this doing laundry?” Etc- and if it happens a few times or is still there for days then maybe we talk a little bit about our expectations for the house and where things go

Tbh I dislike passive aggressive moves like this, instead of conducting a science experiment, just communicate to your partner about maintaining a tidy house, because I know full well the sock leaver has things they tend to leave that the other doesn't like as well.