Use a combination of DeltaYaw() and EntityInView()
Pesudo code:
If DeltaYaw < 0 then object is to left of 'straight ahead'
If EntityInView = false then object is off screen so draw an indicator at left edge.
^^repeat for right-hand edge
etc...
Pesudo code:
If DeltaYaw < 0 then object is to left of 'straight ahead'
If EntityInView = false then object is off screen so draw an indicator at left edge.
^^repeat for right-hand edge
etc...