Historically, I think milk cartons had pictures of missing people on them to increase the chances someone recognized them. It looks like this carton is for a kid's school lunch. I guess with the association with missing people, they figured it was a good idea to give kids some good advice to keep from going missing. Milkwalker is a strange spokesman for the message, though
This feels line the 'YOUR AD HERE' version of putting missing kids on milk cartons. Does the presence of the milkwalker mean no kids went missing that week? Maybe we should want to see the milkwalker more often.
The discolored, worn appearance of the carton takes this to another level of weird. Like it was found in the walls of a house and strange things start happening to the family that found it.