If you're looking for an octagonal one, it's because they don't have one as such. Admittedly, it's on the forward door rather than the back which makes it harder to see from the rear of the train. It's more that one of the leaves of the bifold doors conveniently becomes the stop sign as it folds out. The type 9s, having plug doors, don't have that.Is that the actual reason? Never once, as the driver of a vehicle along the E line, have I ever noticed a stop sign on a train. I just figured I was supposed to stop for a train letting people out into a traffic lane. (Googles pictures of LRVs) ...and I know I know what those look like. TIL
That said, with the type 10 supercars coming it shouldn't be too hard for CAF to include a pop out sign like those on school buses and retrofit it to the 9s.