Do you mean Version 2 screens on regular: local/SBS buses and Express? If so, then the regulars have the Next Stop and ad to it like a rectangle but the Express is square shaped but the Next Stop shows first then the ad blinks a few minutes later. Also, some version 3 screens are on Next Gens with square shapes that won't last long.
For number screen differences, pictures are shown in link, colors on the screen border, text are the differences and voices:
https://twitter.com/Grantcity900K/status/1033826718329528322/photo/1 -> Version 2, Vianova
https://foursquare.com/v/mta-mabstoa-bus-bx23--bx26--bx28--bx29--bx38--q50--bxm7-at-bartow-avenue--coop-city-blvd-section-3--4/4df17a51d22d8c5470d56fad?openPhotoId=5d8d38cd3251e10007306091 -> Version 3, Clever Devices
https://upload.wikimedia.org/wikipedia/commons/3/33/MTA_Bus_653_Interior_Displays_02_-_Parsons_%26_84th_Dr.jpg -> Version 4, Luminator