No, it's just a single quote mark (").
I don't know why my "ANSI" text files do that when they're opened with "UTF-8" coding, but that's exactly what happens, but they reappear when I use Ethan's way of opening them.
The ANSI character set is an 8-bit fixed width ("byte") character set. This means its characters are represented by numbers in the range 0 - 255. All the characters less than 128 are the same as ASCII. All the numbers from 160 to 255 represent the same characters as ISO-8859-1. ISO-8859-1 is the default character set used in web pages, if no other character set is specified in the HTML.
UTF-8 is a multibyte 8-bit character set. This means that, although the unit of encoding is a number between 0 and 255, UTF-8 can use multiple numbers to define one character. The way it does this is by using the top few bits of the byte to encode continuation bytes.
If the top bit of the first byte is 0, for example "A" is character 65, which, in binary is 01000001, then the character has only one byte. All of the first 128 characters in UTF-8 are one byte and they correspond to ASCII. If the top bit is 1, then either it represents the start of a multibyte character, or it is a continuation of a multibyte character. The patterns look like this
110xxxxx => there is one continuation character
1110xxxx => there are two continuation characters
11110xxx => there are three continuation characters
10xxxxxx => a continuation character
The 'x's represent parts of the Unicode code point
An example: The Euro symbol € is not defined in ASCII or ISO-8859-1. It is defined in ANSI though and is character number 128. In Unicode, its code point is 20ac (in hex) In UTF-8, it takes three bytes to define it: 226, 130, 172. In binary, these numbers are:
11100010 => Indicates two continuation characters
10000010 => Indicates the first continuation character
10101100 => Indicates the second continuation character
Another example: the opening "smart" quote. In ANSI, this is character number 145. In binary, it looks like this:
10010001
If you tried to read this as UTF-8, you would see it as a continuation character all on its own. It doesn't mean anything, so Notepad just puts some character in that is meant to indicate "invalid character". In your case it seems to be putting an @ sign in. That doesn't mean there really is an @ there, just that Notepad found a character it can't interpret as UTF-8 and it's a placeholder.
Everybody should be using UTF-8 for everything now. Once we are all doing that, all of these character encoding problems will be a thing of the past.
Once you have got Notepad++, you should start saving your web pages as UTF-8. However, you can't just do that because, as I said, the default encoding for a web page is ISO-8859-1. You need to add
<meta charset="utf-8">
to the head section of each web page you convert to UTF-8 to tell browsers that it is the encoding for that page.