As well as the arrows, the buttons are just positioned intuitively most of the time. We usually get two perpendicular kerb ramps rather than a diagonal one pointing at the centre of the intersection. The button for the crossing you want is the one closest to you or facing you when you're waiting at the intended ramp.
The button gets mounted on its own post if there's not a traffic light pole in the right place to piggyback off.
The button gets mounted on its own post if there's not a traffic light pole in the right place to piggyback off.