I see these boxes all over the place.
They are Unicode characters (two-bytes each) for which your browser is not equipped with a font-set.
It may be a font from a language pack that is not installed.
Those are symbols(and apparently your computer doesn't like those symbols)
You've tried to display a value as text, but it contains doublebyte characters not supported by a character set you currently have loaded. The letters give the numeric value of those bytes in hexidecimal. Either the data wasn't intended to be text in the first place, or it's in some language you haven't loaded support for. I get a fair amount of oriental spam represented that way, for example. If you don't know what it is, you probably don't need to know what it is.