More than likely fallen off, over age and failing adhesive.

Buy a new one, job done.

 

I'm guessing that it fell off as well.
BMW is awfully proud of those emblems - I considered replacing one on my bike (was scratched by the previous owner). I decided that it didn't look all that bad after looking them up.
There are a bunch available for cheap on AliExpress. Who knows about size/quality/durability etc. Same with eBay, but not as cheap. Some apparently OEM.

 

Thanks for the info and feedback. I'll measure and start searching. Glad to hear it wasn't stolen.
Maybe I'll pull the one on the right side and re-apply adhesive.

pete

 

Maybe I'll pull the one on the right side and re-apply adhesive.

That will give you a feeling whether the other one fell off or was pulled off. See how easy it is to remove.
Emblem theft is common - some people collect them and others just like to be dicks when it comes to vandalism.
(Some are replacing ones that fell off or were damaged.)

Personally, I would at least try a pair of cheap knockoffs before forking over what BMW wants for a new OEM replacement.

 

It fell off. The rondel popping off is so common on BMW bikes and more so cars (due to more average sun exposure than bikes) that there are plenty of aftermarket sticker replacements. I should have gone that route when my right side (not surprisingly the sun side when parked at work) disappeared as BMW wants something like $70 for their brand advertising! I think they should give them for free!

 

Yeah, I'm looking at chinese knockoff but i want to make sure I get the right size. The manual says 70mm but I think the sticker part is closer to 68mm. Maxbmw wants $90 for the badge. I won't be replacing it if I can't get one for around $20. MAX BMW Motorcycles - BMW Parts & Technical Diagrams - F800ST (K71)

It looks like it's a 2 piece part and I only need to top piece. I can see the 2 tabs that look like they press into the fairing. I just need the rounded badge.

 

Both of mine fell off at some point. I just bought and installed two new ones.