Well, I guess my question is why would I assume it had any meaning? I assumed it might be a coding mistake or an artifact created by my use of No Script or related functionality, or else an issue created by my browser, or etc, and so dismissed it from further consideration.
Recently there is a trend to use "icons" for stuff, and the icon itself is supposed to convey meaning.
I don't speak fluent "icon". Now that you clarified the situation, or rather you gave me a reason to poke at the little square to see if that made sense of your claim that "X is on the page" - when clearly the thing you showed as being on the home page wasn't anywhere to be found on the home page - I now know that the little square is an icon that means "click here to see something else that you might find useful".
I think this emphasis on icons as communicating "something" has its roots in Apple computers. I think the Apple icon paradigm might be behind Unity and Gnome3 and the more recent Windows desktops, all of which personally I find to be appallingly bad desktops. I suspect icons are widely used in tablets and cell phones. But I don't use tablets or cell phones, and I've never used an Apple computer (well, once, many years ago, for a few minutes), and the last Windows I used before switching to Linux was Windows 2000, which was practically still DOS by today's standards.
So what might be obvious to people who use cell phones, tablets, Apple computers, and Unity/Gnome3-type desktops might not be obvious to everyone else, might indeed present a "discoverability" issue. But I'm guessing most of your website visitors are more used to interpreting icons than I am.