I often wondered myself about "patinated" dials, but who knows what kind of dirt this is:

 

I would say moisture!

 

Perhaps the source is from the under dial?

 

Maybe you are rigth so some kind of glue. Moisture alone leaves no dirt at all, there must have been some kind of chemical reaction. Or is it from the outside, some kind of dust or so? Iam still not sure.

 

Best bet is bringing it to a watchmaker and getting their opinion. I’d imagine there is some kind of hole that connects the UG logo to the dial, which is why I said it could perhaps be coming from under the dial given how many complications are under there, but best bet is going to a watchmaker you can trust. Do your research and you’ll be fine — I recently had to service an old watch for the first time and it was nerve racking but once you get a convo going with the watchmaker, you’ll be able to hopefully distinguish the experts from rookies

 

They are applied with some sort of adhesive - there is no hole through the dial for the logo.

 

Thanks for progressing my learning . Still stand by taking it to a watchmaker for their opinion!

 

They are not applied with adhesive, there are holes in the dial, they are riveted in place.

 

or it's mold and it's ALIVE

 

Whilst the dial you've shown is not a Polerouter dial, I think you are right.

That's not something that I had appreciated before. I have lots of pictures of the reverse of Polerouter dials and there are holes where the logo is riveted in place. The holes are often small and not at all obvious but they are there on closer inspection.

 

youre right, the loose dial i looked at was painted black on the back - looks like theres either 1 or 2 holes where the logo is joined.

 

Thanks for sharing, good to know....that I was right Really does a lot for my confidence on this fine Sunday morning