If it's aftermarket its at least 20+ years old because it was my great grandfathers, and he collected odds and ends. I found it in one of his old tool chests. The mirror will swivel. Its mounted with 2 set screws. The arm is aluminum if this helps date it. It seems automotive to me but idk
Many many many parts stores sold those. They clip onto the door edge and you just tighten the set screws to hold it in place. They were not for any specific car, but were sold by places like JC Whitney, Western Auto, Sears, Monkey Wards, JC Penney etc, etc to go onto any & every every car. My Dad had one on his '49 Chev and another on his '50 Dodge. My Grandfather had one on his '48 Studebaker. Setscrews had a habit of stripping and the whole thing would fall off while driving. They were available right up into the 60's when manufacturers were required to put fender/door mount mirrors on the left side of new vehicles. Some folks mounted them at the top of door, some mounted them at the "bottom of the window" level.