Thus the replacement character is now only seen for encoding errors, such as invalid UTF-8.

At one time the replacement character was often used when there was no glyph available in a font for that character. However, most modern text rendering systems instead use a font's .notdef character, which in most cases is an empty box (or "?" or "X" in a box[5]), sometimes called a "tofu" (this browser displays 􏿾). There is no Unicode code point for this symbol.

The replacement character � (often displayed as a black rhombus with a white question mark) is a symbol found in the Unicode standard at code point U+FFFD in the Specials table. It is used to indicate problems when a system is unable to render a stream of data to a correct symbol.[4] It is usually seen when the data is invalid and does not match any character:

By the way, I am not talking about � (replacement character). This one is displayed when a Unicode character could not be correctly decoded from a data stream. It does not necessarily produce the same glyph:

replacement glyph

U+25A1 □ WHITE SQUARE may be used to represent a missing ideograph

The character exists in Unicode/ISO 10646, but not in the character encoding used for the document. In this case, use Numeric Character References (NCRs, example: 噸).

However after doing a bit of testing I see that this character is not used to represent missing glyphs on either my Windows 7 computer or the Android phone I've tested with (Motorola Atrix).

The Unicode replacement character sounds promising when reading about it on Wikipedia: It is used to indicate problems when a system is not able to render a stream of data to a correct symbol. It is most commonly seen when a font does not contain a character, but is also seen when the data is invalid and does not match any character