I can’t tell from your picture but the correct orientation is marked on the board.

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Looking at the schematic, it seems sometimes the positive and sometimes the negative end of the cap goes to signal ground

I assume that you are referring to things like C2 & C204? The schematic makes sense since the negative" lead of the capacitor is connected to a voltage lower than ground. This would keep the electrolytic capacitor (properly) forward biased. I can't tell if how the capacitors are installed on the circuit board are correct. Markings on the board are usually accurate, but not always. Mistakes happen in printing the boards and I don't blame any manufacture for not scrapping boards for this kind of mistake. Same goes for printed schematics. Many times they "fix" the issue by an obscure errata statement. The best practice is to install new capacitors with the same orientation as the original ones. Taking "before" pictures of the circuit board can be really helpful as part of the quality control or debugging process. If all else fails, verify that the electrolytic capacitors are forward biased with a voltage measurement. Glitch  

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If all else fails, verify that the electrolytic capacitors are forward biased with a voltage measurement.

Thanks. I don't think the markings are incorrect, I just found them somewhat counterintuitive. Thanks for clarifying. I also found some old pics in the archives that have helped confirm.

I realize that, it's just that on at least one of these caps, the positive goes to the solid, filled-in side of the label, whereas normally, the solid part of the label indicates negative (-).

The "solid" marking indicates ground.
That's not necessarily the capacitors negative pin because some capacitors work with negative voltages.
The best reference is what the factory fitted (though that is not always guaranteed to be correct either).

Martin