Custom Asset Icons?

I’ve just learned how to make custom assets, and I’d like to give them a special icon instead of the default paper-with-bent-corner icon. Just as Terrain assets have that little island with a palm tree, I’d like my different assets to be distinguishable.

How might I go about that?

Check out this answer

Where did you go to find out how to make custom assets? Can you share the link, or summarize the technique here?