Yes those are the master spline indicators. The coupler will only slide down onto the main stub when the two master splines are aligned. .
This is so that the steering wheel will be in the correct position to center the sector shaft on the rack and put the steering box in the center of its travel where it's sensitivity is the lowest. This so you won't have to chase the car all over the road while trying to cruise in a straight line. If the car does not steer straight ahead with the splines correctly engaged and the steering wheel correctly oriented, then the tie-rods are not adjusted correctly.
If you ever remove the steering wheel,you will find a similar methodology there; Master splines that have to be aligned to engage.
