A purple cow with a bell on a yellow circle in the center, yellow text on top and trademark at lower right on a white background.
A “Magic Cow” is a drink made by mixing a powdered soft drink mix into milk. It was created by the National Dairy Council as a way to promote drinking milk to kids by making it fun and more appealing with flavors. You also could buy mail-order shaker cups.
You can see one of the commercials here https://www.oddballfilms.com/clip/13160_13314_american_dairy1