I am creating a map of protected areas/parks and want to display a letter label (A, B, C...) inside the polygons of all the parks in the map. The full names of the parks are too long to fit inside their respective polygons and make the map look cluttered. I know I could add a new field to the park layer's attribute table and type in the letters manually line by line, but since I have to repeat this process for several maps, I am seeking a more streamlined way to do this. Ideally the letters would appear in order on the map from left to right (W to E) and top to bottom (N to S) for easy reading, though that's not a requirement. I can't use the first letter of the parks as their label letter, since there are a lot of the names start with the same letter.
My goal is to create a map with the label letters inside the polygons, and then have a reference table with the letters, names, and other attributes on the side, where there's more room to write them out.
I'm working in ArcMap 10.6.1.