The way I interpret omens comes from my family’s practice. Personally, I don’t believe in making up your own meanings. It’s not for me. I don’t think it works for me. But hey, if you think it works for you, go right ahead.
I don’t have a book or source for you. But I know they’re out there. And, to answer your question about appropriation, it wouldn’t necessarily be appropriative to do that but every region has its own omen sets for a region. A lot of times omens are actually just noticing patterns. For example, around here, sparrows weaving baskets in the air is a sign of rain to come. In other regions, wrens weaving baskets in the air is the same sign, but sparrows have a different significance. Another example—you wouldn’t see what’s commonly referred to as a vulture around here. Buzzards, on the other hand, we have.
Every region has it’s own ecosystem. Different plants and animals for every area means different ‘omens’ for different areas. Similarly the symbolism of directions is likely to differ based on your relative location to other things. Here, if the geese land in February, it’ll be hard summer. In other places, this wouldn’t be accurate.
You see what I mean?