It's environmental damage. The coin has a layer of scuz which became streaked when it got rubbed in a linear fashion. Alternately, this discoloration may have brought out impurities in the metal, causing it to tone inconsistently, in such a way that the striations became visible. Either way, it's worth a quarter. But you're right- it does indeed look as though that horse is standing in the rain, which is kinda fun.
Environmental Damage I find quarters like yours when I metal detect. The green stuff around his nose are not boogers.. More like grime.
There are now FOUR (by my count, so far) completely different words that many people are trying to get us to use interchangeably, and it's not just wrong, it's outright harmful to the hobby. Vocabulary needs to MEAN things, and it needs to be important. Here are my four "word candidates": a) error b) damage c) variety d) oddity If we throw these words around willy-nilly, we are damaging our entire hobby. We need to stand steadfast against using these terms sloppily.
I agree with this, as I have pulled quite a few from new rolls. This coin though, will only be worth a quarter because of the nasty stains and stuck debri on the surfaces.
another good reason not to collect 21st century cents and clads - a century from now, they will have completely disintegrated if left exposed to the elements