When the bottle doesn't say, how does one know when to refrigerate sauces?
For example: soy sauce, fish sauce, etc.
I usually assume that if the bottle doesn't specify (and you bought it off a shelf, not out of a refrigerated area), then it's safe to store in the cupboard. You can also ask at the store if you want to be sure, though I suspect unless it's a small, specialty store with knowledgeable personnel, they will err on the side of caution and just tell you to refrigerate it.
For your specific examples: Soy sauce is definitely fine to store in the cupboard, though some brands will recommend refrigeration for "best quality". Fish sauce I'd usually store in the fridge once opened.
funny -- until you mentioned this, i never realized my own hypocrisy: i store soy sauce in the fridge, but fish sauce in the cupboard. i now realize that i should probably choose a side and stick with it, haha. both are so high in salt, it's probably fine to store them in the cupboard, but it certainly wouldn't hurt them to keep them in the fridge.