Vintage BMW Motorcycle Owners

This is a well-known picture of journalist Marianne Weber in 1952, putting an R68 through its paces. (When told the new bike could do 100mph, she jumped on and got it to 99mph--in civilian clothes, with no gear other than gloves!).
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In looking closely at this pic, there appears to be something on the far side of the headlight shell.
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What is the round object that can be partially seen? It almost looks like a horn, but makes no sense for one to be mounted there. I've looked at various R68 manuals/pics, and have never seen anything attached to the headlight shell on that side. Am I looking at the picture wrong? What could this be?

Good eye.

A tax disc, maybe?

-Chris

>A tax disc, maybe?

Wow! I googled "tax disc vintage motorcycle" and this was the first picture I got:
Change the mounting angle a little bit and it certainly looks likely! Using the headlight mounting bolt appears to have been standard practice. This is obviously an instance where the factory manuals/parts lists would not provide any insight, so a little 'real world' knowledge goes a long way in filling in the holes in my understanding.

Thanks for the quick ID, Chris!

There are a few listings on eBay with more pictures, too -- but none quite matching the back as in the main photo.

I wonder whose bike this was? Are there more photos of it? Does a tax tag imply only UK? I wasn't able to find a good source for the full story here - only what's been briefly repeated over and over.

-Chris

She was a Belgian journalist and was supposedly reviewing the bike for a French magazine; her review is supposed to appear in the Aug 1952 edition of Motorcycle (Motorcyclist?) magazine. Couldn't find a copy, but it would be in French anyway; that article would probably answer your questions.
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This is a very similar 1951 picture of her on a Vincent Black Shadow, where she got it up to 112mph! Again, no helmet, but at least she had real motorcycle boots and gauntlets. The picture was taken by the owner of the motorcycle.
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She was one of the first to organize motorcycle rallies/tours for cycling enthusiasts in Europe after WWII.
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I'll bet she was cool as hell!