The element inspector shows those Unicode characters as "alt" description for the missing pictures.
It seems Chromium based browsers additionally notify the user about unavailable pictures with a placeholder. The characters look differently for Chromium browsers and on Windows compared to the example in spoiler above)
As a reward I'll tell you what I know; not much sadly.
The emoticons should be delivered by a third-party (twemoji.maxcdn.com), an URL I can't open now. It seems the browser falls back to integrated Unicode chars for the font currently in use to rudimentary show something