Behind the Steering Tiller on the Capt side is a round plate with in the middle a round opening through which a Steering Tiller.

On the right-hand side of this picture there is a decal (sticker) attached with the headings LEFT – CENTER – RIGHT.

The F/O side, there is also a provision for a Steering Tiller, but this place is usually sealed with a full around picture.

More info and photos : http://www.flightdeck737.be/hardware/platform/zijpanelen/inopbouwonderdelen/