We haven't had an explanation what DRN stands for as yet, so you won't find it while rewatching!

DRN doesn't always have to stand for something. Like in cars, a Toyota Camry LE. LE doesn't necessarily stand for anything, it's a model name. The same probably goes with a DRN. Although, I've wondered if Dorian, a DRN, was named Dorian because of how close DoRiaN is to DRN- the letters in DRN spread out into Dorian's name.