@n.chiri, the arm is actually above the structure gauge, so the trains pass below it. A "mirrored" arm is unrealistic and would be dangerous in real life because a signal with the arm pointing toward the other side is a signal valid (only) for trains heading in the other direction.

I wish semaphore signals could be more easily mirrored as it doesn't feel right to have their arm protruding into the loading gauge when displaying danger. Especially in an American setting where trains are much larger.