The phrase «Μηδείς αγεωμέτρητος εισίτω μοι την θύρα» (or «Μηδείς αγεωμέτρητος εισίτω μοι την στέγη») is a phrase that supposedly was on the threshold of Plato's Academy and translates to: "do not let anyone ignorant of geometry through my door" (or under my roof). See for instance this discussion https://www.plato-dialogues.org/faq/faq009.htm

The phrase in AMS' logo translates to "Do not be ignorant geometry".