The Grunge YouTube channel recently posted a video about the relatively short-lived trend of putting pictures of missing children on milk cartons.
Mostly popular during the late 1980s this trend is virtually never seen anymore. As the video explains this is due to a combination of factors such as more common use of plastic containers, the creation of the AMBER alert system and issues of whether putting pictures of missing kids on milk cartons was ever effective.
I remember seeing those kinds of milk cartons. Mostly though I remember this being part of a plot for a Small Wonder episode; which cracked.com refers to as one of the darkest episodes of a 1980s sitcom.