Can you see the ones in Joe's original post and Jeri's?

If so I think it's because some browsers recognise those - the unicode block starting at x1F600 - as emojis and handle them differently - applying a special emoji image set.

Grishka's emoticons are symbols, and are displayed using the website or default browser font. That's why you can colour them with a font color tag - you can't do that with the x1F600 emoji.

So my guess is that whatever font you're displaying this page with does not have glyphs for those symbols.

(I notice that Jeri's emoji looks deranged on an iPad but quite friendly on Android. What on earth does it mean?)