Blue eye spot - In my experience NEVER present on stocked fish. Usually present on wild fish. So if it has it, it's wild. If it doesn't, you can't be 100% sure. From my understanding this forms from diet very early in a trout's life, just after hatching. But, this spot sometimes doesn't show up great on camera, unfortunately. Reflective things are funny, depends on the angle.
Red - spots, fringe on the adipose. We're not talking orange. We're talking red. And it's NOT a reliable indicator as it's only usually present on wild fish and usually not on stocked ones (unless fed a special diet by a co-op or something). But it's diet based. And older browns can become mainly piscavores and often lose the red, while stocked ones can start feeding on a bunch of shrimp or something and gain it, though usually if it starts later in life it seems not to be spots but more fin fringes and the like.
Black spot patterns - Not reliable either. But this is pure genetics. The PAFBC's modern stocked brown trout tends to have squarish black spots, and lots of them, right on down through the lateral line. Wild stocks vary widely owing from different periods in which the wild population was "seeded". But if sparsely spotted it's probably wild. A common "wild" look is denser round spots down to the lateral line on the front of the fish, angling up and only on the back in the rear. There are streams, though, where the black spot pattern on wild fish is very similar to the PAFBC's stock.
Fins - Yeah yeah, stocked fish often have beat up fins. But, but, fins do regrow, albeit slowly. So a long time holdover, or a fingerling stocker, can have good fins. Also, conditions in co-op hatcheries vary widely, and some are better than others. Also, older wild fish start to get beat up after a while in some locations, as like in humans, growth/regeneration decreases with age but "life experience" increases, lol. So this is another non-reliable one, but a decent general rule of thumb one.
Location - Should there be wild fish here? Should there be stocked fish here? Not 100% reliable either. Fish move. And some places should have both or neither!
Overall coloration - least reliable. We're talking about that "butter" color, as well as any vertical barring. Purely diet based, and changes quickly with a change in diet (as in a few months, based on my observations). Wild fish can be pale and stocked ones can color up. But, color is the first impression on viewing a fish and it's probably 70% accurate.
Most of the above lead to a pretty good conclusion most of the time. i.e. none of them alone is 100% reliable. But if the vast majority of the markers are one way or the other, then you can be pretty comfortable saying one way or the other. If you've got 6 markers of wild that are 80% accurate each, and 0 of stocked. Yeah, it's wild.