jQuery: Detect if element exists

Question

In my code I have the following html that gets appended to a List Item when the user clicks on a specific element.

<span class="greenCheckMark"></span>

Using jQuery, how would I detect if the element existed, and if so, not add another green checkmark?

$('.clickedElement').live('click',function(){
//does the green check mark exist? if so then do nothing, else 
$('#listItem).append('<span class="greenCheckMark"></span>');
});

Answer 1

Use not and has

$('#listItem:not(:has(.greenCheckMark))')
    .append('<span class="greenCheckMark"></span>');

Answer 2

You could just look for it?

($('.greenCheckMark', '#listItem').length > 0) ? /* found green check mark in #listItem */ : /* not found */ ;

EDIT: Fixed 'un-relatedness' to question.