When Android devices cannot locate a suitable shortcut icon, it will add a tile with the first letter of your website’s url. This is a missed branding opportunity, where your logo could be appearing.
When iPhones cannot locate a suitable shortcut icon, they will add a miniature image of your website. This is a missed logo opportunity, and can be confusing to the user.
Windows can pin your Website’s logo to the taskbar. If a suitable shortcut icon cannot be found, Windows will use the Internet Explorer logo for the link. This is a missed branding opportunity for your organization.
Chrome for Windows and Chrome OS both allow for website url logos to be Added to the Shelf, or pinned to the Taskbar. When appropriate icons cannot be found, a letter tile is used in place of the logo. This can easily be corrected.
Chrome OS – Chrome Added to Shelf