I have just come across this website (http://helios.io) that has an icon IN the title. Not a favicon, but next to the title text (on the right of it).
How was this achieved?
(worked in both Safari and Chrome)
That would be the Unicode character U+1F680
.
You can find it here, using the handy Unicode Character Search:
http://www.fileformat.info/info/unicode/char/search.htm?q=rocket&preview=entity
on your Mac, it's rendering used the built in emoji font - a preview is here: