All standard torsion bars supplied by Porsche should be marked Left and Right and it is prudent to install them in the correct orientation.
If the bars are unstamped they are likely to be aftermarket and in general if they are unmarked it doesn't really matter.
The reason for the marking is simple -
It is custom and practice when making new springs that they are loaded to virtually coil bound in the case of coil springs and to just past their yield point in the case of leaf springs and torsion bars.
This process is known as 'scragging' and is generally part of a final test procedure and in my experience all springs produced by car makers are 100% tested. this procedure is some times called presetting but always involves some plastic deformation.
scragging or presetting - IEC
When a torsion bar is scragged it is twisted to just beyond it's yield point which effectively increases the strength of the material but does not change the torsion bars spring rate spring rate and this creates an unusual condition.
If the torsion bar is then used in the opposite torque helix the yield strength of the material reduces slightly and this is known as a Bauschinger Effect.
In extreme circumstances this could affect the fatigue life of a torsion bar but in practice I think that the effect would be insignificant and I wouldn't worry.
Some after market torsion bar manufacturers claim to preload torsion bars to 90% of their yield strength and from a metallurgical perspective this may help to eliminate any initial set as it it will help to transform any residual austenite but there would be no need to mark the springs left and right as loading to less than the yield point will not create a Bauschinger Effect.
If you can't tell which bar is which I would not be greatly concerned.
