Bitcoin defines a protocol for that, and you can use that part separately from Bitcoin and it works, like Litecoin or forks of Bitcoin. That's not the part we're actually referring to when we say 'Bitcoin'. That's not what the icon means.

In Nostr, the icon means the client. Though maybe HTTP should have an icon. Maybe it doesn't mean anything at all regarding having an icon. Maybe we need an icon for a protocol for making social apps.