Basic Trope: A child goes missing, and his/her picture and info is put on a milk carton.
Straight: Alice is missing, and her parents file a police report and soon after, Alice's picture is seen on every milk carton.
Exaggerated: Alice's picture is on every billboard, every grocery item except produce, every telephone pole, etc.
Downplayed: Alice goes missing, but because her hometown and/or population is rather small, she's only seen on one milk carton/billboard/whatever within that town (because they also don't have good media outreach).
The story takes place during The Eighties or some other such time before Amber Alerts, or in a place that simply does not have them.
Alice is a cow, and her picture is therefore already on the milk cartons.
Everybody sees the picture, but no one seems to care that Alice is MIA. (Some might even be happy about it!)
Alice was missing as a child or teenager, but she has since been recovered... Although the dairy company apparently hasn't gotten the memo, because the photo has been on every milk carton for the last 20 years.
Lampshaded: "I want my baby's picture on every milk carton until she's brought home safely!"
Defied: Alice's parents don't send a photo to the dairy company, for any number of reasons.
Deconstructed: This is not the most efficient means to alert people that a child is missing. (Especially when you consider the article on The Other Wiki that states that stranger abductions usually end with the child being killed in the first three hours, and that a lot of the reported cases were parental abductions such as that mentioned above, misunderstandings, or even outright hoaxes.)
Reconstructed: A better, more efficient system is put in place, so that abducted or lost children can be found more quickly and easily.
Played For Drama: A Lifetime Movie of the Week in which Alice is abducted by a pedophile and it's a race against time to find her.
Played For Laughs: Alice's parents are overreacting and they only have silly costumed photos of her.