What does the AOE notation on the sectional stand for? This appears at the bottom of the information for an airport as the final line.
It stands for "Airport Of Entry" (see VFR Terms) In other words there are customs facilities there.
All civil, private aircraft entering the U.S. must first land at an airport of entry before continuing to their destinations, unless other arrangements are made with U.S. CBP. Advance notification must be provided electronically to CBP by means of the eAPIS. See the APIS section for more information. (source)
To my knowledge this is also common for international operations outside of the US/FAA jurisdiction although im not sure how its marked on various maps elsewhere.