It's not in the html text, so I guess it might be that the ISP's httpd send the icon info to IE via http header, which is not visible even if you view the source.
It's been a long time since
I wrote a simple http parser(http2.0), maybe they have come up
with something new in IETF, or it's just stupid MicroSoft's proprietary
header... sigh... , lemme check RFCs.