You never gave an idea on the quantity, but I would imagine one of 2 options, a window, or a void with a sticker, as they seem the common ones.
If your ordering around 100 units of an enclosure, talk to the manufacturer, generally its not to hard to have them punch out the windows for you with a specialised part number. A recessed window would cost more though
Second approach is similar, just using a high grade clear sticker over the display cutout for a window, I've seen this method used over and over again in automotive diagnostic tools