I noticed on my website, http://www.cscc.org.sg/, there's this odd symbol that shows up.
It says L SEP. In the HTML Code, it display the same thing.
Can someone shows me how to remove them?
That character is U+2028 or HTML entity code 

which is a kind of newline character. It's not actually supposed to be displayed. I'm guessing that either your server side scripts failed to translate it into a new line or you are using a font that displays it.
But, since we know the HTML and UNICODE vales for the character, we can add a few lines of jQuery that should get rid of the character. Right now, I'm just replacing it with an empty space in the code below. Just add this:
$(document).ready(function() {
$("body").children().each(function() {
$(this).html($(this).html().replace(/
/g," "));
});
});
This should work, though please note that I have not tested this and may not work as none of my browsers will display the character.
But if it doesn't, you can always try pasting your text block onto http://www.nousphere.net/cleanspecial.php which will remove any special characters.