73 E Targa additional "option"plate decode please

[Toxyman]

Hi there

I've searched pretty well most of my usual links, and this forum, but cannot seem to find any info on the extra plate I have above the VIN plate on my 73 911E Targa, so I hope someone can help me

the vin works out correctly, but above it, there is an additional plate with "BS AU 48" on it - it seems to have been placed there at manufacture...

This is an early RHD model, Currently in New Zealand,

Anyone with any ideas please post!

PS - yes I know it's been repainted, it was 018 Tangerine - one day I might change it back...

Cheers

Chris