White Square 9633 □
Small White Square 9643 ▫
However, what you see on this forum, and in some other places is probably just the default nul character, which is used if a character is not available in a given character set. This forum uses charset=iso-8859-1 click here which lacks characters like curly quotation marks. When people paste messages from Word, they contain curly quotes, which get displayed as white rectangles.
If you want a genuine white rectangle, you should use the Unicode Geometric shapes with a suitable font, like Lucida Sans Unicode. You can insert these in Word from the Insert symbol dialogue, or type the Unicode decimal codepoint on the numeric keypad while holding down Alter: This works in the message box because I am using Opera, but it may not work in Internet Explorer, and the square rectangles which are different sizes may be replaced with nul characters on posting the message. ? ?
So now you know, I bet you wish you never asked.