You mean like an aircraft's 'horizon ball' thing ?? If Poser cameras have that, sorry, I cannot find it...

FWIW, a two-minute whatsit: Library, props, Poser primitives' box. Drag into scene. Select box_1. Scale to 50%. Duplicate. Select box_1, duplicate again.  Select box_1, x-scale 500%, xTran positive until just clear of #2 and #3. Select box_2, y-scale 500%, yTran positive until just clear of #1 and #3. Select box_3, z-scale 500%, zTran positive until just clear of #1 and #2. Colour-code #1~~#3 to taste. Their 'show in ray-trace' [  ] (no) only seems to work for Firefly, which is unfortunate...