When I'm downstairs and come across an item that belongs upstairs, I put it at the edge of a stair so the owner can collect it on their next trip upstairs. Be it pens, papers for the office, books, school work, socks, hair clips... if it's small enough to go on the stairs it sits there to be taken upstairs. Don't most normal people do this?
Whenever I climb the stairs I pick something up and drop it in the appropriate room (bathroom, office etc). I don't take the kids' stuff up now they're all over 14 because they don't like me going in their rooms when their not around. Fair enough.
My husband, sons and daughter all walk straight past everything each time. Even when it's their things. My brother does the same at his house, walks right by it without a glance. Drives my SIL nuts.
IABU - yes, this is some secret witchcraft code only mothers know so obviously you have to ask them speciffically every single time
IANBU - no, the lazy numpties should get their arses in gear, you are not domestic staff.