You can get mobile devices to use a nice looking icon for your website when the link is placed on the home screen or a favorites page. The data is supplied through the mobile device in the form of a JSON file, containing information about the resolutions and devices you have made avaialble. The web app manifest is described here: https://www.w3.org/TR/appmanifest/ and at the time of writing isnt finalized yet (tho it seems to be used flawlessly by any recent android and ios device). Example file:
{
"name": "App",
"icons": [{
"src": "/android-icon-36x36.png",
"sizes": "36x36",
"type": "image/png",
"density": 0.75
},
{
"src": "/android-icon-48x48.png",
"sizes": "48x48",
"type": "image/png",
"density": 1.0
},
{
"src": "/android-icon-72x72.png",
"sizes": "72x72",
"type": "image/png",
"density": 1.5
},
{
"src": "/android-icon-96x96.png",
"sizes": "96x96",
"type": "image/png",
"density": 2.0
},
{
"src": "/android-icon-144x144.png",
"sizes": "144x144",
"type": "image/png",
"density": 3.0
},
{
"src": "/android-icon-192x192.png",
"sizes": "192x192",
"type": "image/png",
"density": 4.0
}]
}