I used Lyx (a Latex distribution) to convert my content to an HTML page.
I noticed that the sigma symbol represented in firefox is composed of these 2 characters: ⎲ ⎳
The first character is for the upper part of Sigma symbol, and second character is for the lower part. I tried to search Google for these "weird" characters but could not find anything. Do those characters even belong to ASCII? Can somebody tell me where I can find those weird characters?
It are characters which are specified by Unicode which can cover over one million characters. Practically every character the mankind is aware of is specified in there. You can find details about specific Unicode characters at fileformat.info search.
⎲is the Unicode Character 'SUMMATION TOP' (U+23B2)⎳is the Unicode Character 'SUMMATION BOTTOM' (U+23B3)
In order to be able to use them, you've to use an Unicode compatible character encoding, such as UTF-8. Using a different character encoding to present them would only result in Mojibake.
They're unicode (2-byte) chracters. If you know the encoding scheme, you can probably figure out what they are, likely UTF-8.
They are the Unicode characters U+23B2 SUMMATION TOP and U+23B3 SUMMATION BOTTOM. They do not belong to ASCII, no.
来源：https://stackoverflow.com/questions/7890398/what-are-these-characters-%e2%8e%b2%e2%8e%b3