What is the symbol  ? It keeps appearing on twitter.?

[Zender]

What is this symbol?  It keeps appearing on my friends twitter posts. Is it like an error for text symbol/character they are typing, and if so why am I seeing it?

[MegaGames.DK]

Example, twitter is using american keyboard. If a guy uses an arabic letter, it we have the errorsymbol 

[Gumblar Martuz]

It's a Special type of letter and if it comes up with that Square then your Computer doesn't have that character installed.

Hope I helped.

[Jallan]

Using the FIrefox web browser, that comes up as a box with the characters E418 inside it. That means that Firefox cannot find any font containing this character on my system, and therefore is showing me its Unicode number so that I can look it up.

So I type E418 into the query box at http://www.unicode.org/charts/PDF/UE000.pdf .

This tells me this is a character in the Private Use Area which has been set aside for font makers to use for any character they wish. Some of your friends may have a font in which the font creator has assigned the code point E418 to a character.

Some font creators use the Private Use Area for variants of symbols encoded elsewhere or for parts of symbols encoded elsewhere. The Private Use Area is also used by the Conscript Unicode Registry which allows people to register characters in this area to prevent overlap between private scripts in fonts. See http://www.evertype.com/standards/csur/niskloz.html . But the Conscript Registry is not “officially' recognized by Unicode which declares that anyone can use the code points in a Private Use Area for any purpose they wish, regardless of how someone else may have used them.

Characters in a Private Use Area should not be used in a common forum but should be restricted to special-purpose forums where certain fonts are expected to be used.

If the symbol you posted just looks like an empty box or bullet to you, then it is probable that you have actually been seeing a number of different characters that are alike only in that none of them matches a character in your fonts or, at least, the character is not being picked up by your browser.

I suggest trying Firefox, if you are not already using it. Firefox does the best job of font substitution in my opinion and at least shows you what the number of the character is when it can’t display it.

In some cases a non-existent character may just have been inserted in error by the person who created the message. In other cases the person may be seeing a character in a font that he or she has on his or her system and is not aware that this is non-standard usage.

In some cases, you may just not be seeing a character that some others are seeing because you lack a font to display it or because your browser is not finding that font.

Good fonts for the Latin alphabet that contain lots of symbols and other characters are the free DejaVu fonts from http://users.teilar.gr/~g1951d/ .

See also http://www.alanwood.net/unicode/fonts.html for more fonts that contain a large number of symbols or characters used in a particular language, most of them free.