The design was inspired by the Contacts.app icon, Moleskine, and elephant skin. It includes 2x retina resolution, up to 512px.
The simplest way to use the icon is to drag and drop the linked icns file onto the default icon in the “Get Info” window: find Evernote.app in the “Applications” folder; open “Get Info” on it with ⌘I (or find it in the “right-click” context and “File” menus); and drag and drop (or copy and paste) the preview icon in the top left with the new icns file. To revert to the default icon, select the preview icon and “delete.” Relaunch Evernote to effect changes. You’ll need to apply the icon each time the application is updated.