Q:

Windows OS displaying unknown character vertical rectangles in browsers

I had an interesting issue pop up today on a couple of websites I host. Specifically a vertical rectangle character is displaying (mostly) near  characters in my code (though I tend to use those sparingly) but only on Windows machines. I've only seen one instance where that the vertical character has displayed in the middle of a paragraph. 
I checked the site in Firefox, Chrome and Safari on Mac and didn't see any issues. Even more interestingly, when I log in to the site backend on the Windows machine, the vertical rectangle character is actually selectable and deletable. No clue why this is happening. 
Both sites are running on Wordpress. I've attached a screenshot for reference. Thanks!
Unknown Character Reference Screenshot

A:

That is a character that your font doesn't know how to render properly. Try to copy and paste it into google, and see what it says it is. Chances are it is safe to remove it, try retyping that bit of information WITHOUT copying and pasting. Else, try a different font and see if it is still there. See this for more; specifically: The replacement character � (often a black diamond with a white question mark or an empty square box) is a symbol found in the Unicode standard at codepoint U+FFFD in the Specials table. (Bold Added)

