Cruisin' on my Bluebird
Sturmey-Archer produced those covers, I believe they're still available. The purpose was to protect the indicator chain and keep dirt out - a nice touch but the hub will work without it, so a lot of them were probably tossed. I've seen earlier versions that were aluminum, and that might have been what was originally on this bike, but I don't know for sure. I don't know what year they went to plastic.