Use a feed icon included with the app (instead of the app icon) as the icon for NetNewsWire feeds.

Mac/AppAssets.swift

@@ -48,6 +48,8 @@ struct AppAssets {
 		return RSImage(named: "accountTheOldReader")
 	}()
 
+	static let nnwFeedIcon = RSImage(named: "feedIcon")!
+
 	@available(macOS 11.0, *)
 	static var addNewSidebarItemImage: RSImage = {
 		return NSImage(systemSymbolName: "plus", accessibilityDescription: nil)!

Mac/Resources/Assets.xcassets/FeedIcon.imageset/Contents.json

@@ -0,0 +1,23 @@
+{
+  "images" : [
+    {
+      "filename" : "FeedIcon 2.png",
+      "idiom" : "universal",
+      "scale" : "1x"
+    },
+    {
+      "filename" : "FeedIcon.png",
+      "idiom" : "universal",
+      "scale" : "2x"
+    },
+    {
+      "filename" : "FeedIcon 1.png",
+      "idiom" : "universal",
+      "scale" : "3x"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}