Hi there, the older early - mid 80's powerlite bars were not stamped in the grip area,
Here is info I have been able to assertain (Please jump in anyone if you have any more info, or anytthing here is not quite right)
1. Earliest Powerlite Bars, round Decal facing rider on right hand site of bar. White background with a Red P in the middle - Probably until about 1982. Alloy bars used thinnner alloy than the later powerlite bars and had a thinnner crossbar, no stem knurnling.
2. Mid 80's powerlite bars, Mid 80's Powerlite Bars, round Decal facing rider on right hand side of bar. chrome background with a Red P in the middle - chequre bacgound.
(VDC also did a run of bars for powerlite. Uses exactly the same decal as no 2. But in small writing under the red P it says (approved for powerlite) should also have a vdc decal on - here is an example.

Late 80'd powerlite bars, stamped in grip area, yellow p oin right hand sode of bars facing away from rider. Stem Knurnilin, thicker crossbar (Mini Bars, thicker alloy)
Thanks
JW