The Professor Willow design is a parody of the iconic Dr. Pepper logo. If you don't know who Professor Willow is he is a character in the game Pokemon Go. In the beginning of the game he is the one who greets you to the Pokemon world, and who you later transfer Pokemon to for candy.
Wizards, Muggles, Aurors, Half Giants and Death Eaters all enjoy the refreshing taste of a hot, cold, or frozen Butter-Beer. I'd like to buy the Wizarding World a Butter-Beer and teach them all to smile. Only 2 sickles at Fountains and in Bottles (though Muggle prices may be higher in some locations). So go ahead, open frothy happiness. Always Butter-Beer.