How Twitter.com set Apple Touch Icon? Can I use OS X to discover and scrape a web site favorite icon for later reuse? (and I'll deal with any licensing issues if needed - just looking for how to do this for personal use currently)

Similar to the Favicon, the apple-touch-icon.png is a file used for a web page icon on the Apple iPhone, iPod Touch, and iPad.
According to Specifying a Webpage Icon for Web Clip there are two ways to set the Apple Touch Icon:
One is to put the apple-touch-icon.png on the root document folder, another is using rel="apple-touch-icon" to add a link element to the webpage. However twitter.com doesn't use any of those methods. 

How can I find twitter.com's apple touch icon URL using Safari 8.0 on OS X Yosemite?
I find that's Apple Safari behaviour.It use iPhone UA to get Mobile Webpage,that have Apple Touch Icon in link rel.