I really want to just go put something under the wheels but I’ve never talked to these people.
Update edit: thank you for all the replies. I went over and knocked but no answer. It’s definitely not chocked. If I see them come home I’ll go back over. I’m worried as soon as the weight shifts loading it that it will just go down the hill.
Chock the wheels and leave a friendly note on the hitch if nobody is home IMO, I seriously doubt they would take offense.
This is what I would do.