How Do I Know it's Retro ? And, Why?

McD’s just gave my wife and I our dinner to go in bags donning a winking burger, single arch, etc. Maybe you’ve seen this, too. And yet, how is it that we both seem to know without a doubt this is a retro-look for McD’s, and not some new logo? What is it about this style that screams “retro” from an age prior to our existence? - Jinx