I think because dvd's are read-only, you cant tag the folders with a media type. You could force everything to large icons, e.g. set everything to General Items and force the view to large icons and apply to all folders.
Or stop using DVD's because they can get scratched and so are a risk of data loss. Go an order a nice new external hard drive and move all your dvd's onto the external drive. you can a get nice 2.5" passport drive for quite cheap. A 1TB drive would have enough space for 250 of your dvd discs.