Weird graphic has appeared next to menu items with dropdowns

On my primary navigation bar, any menu item that has dropdown items below it is suddenly displaying a weird little graphic next it (almost like it would be a dropdown arrow, but instead it's a little square with some letters in). There was nothing there before. This is not a new site or new theme. The theme is up to date. There is nothing in Customize > Menu or Widgets or elsewhere on the dashboard that I can see to add or delete or alter this in any way. Any idea what's going on or how to get rid of these?