In a User's Private Message Inbox is a column where people can "flag" a Message.

I am in the process of adding the ability to sort by this column.

In the Column's Heading, I have a Flag icon that I found on WikiPedia Commons.

Is there some way to *visually* add an HTML hyperlink beneath the icon so people will know to click on it if they want to sort on that column??

Here is a code snippet...
HTML Code:
	<th id='colFlag'>
		<a href=''>
			<img src='/images/red_flag_icon.png' width='15' alt='' />
Unfortunately, you can't see a hyperlink below it, which is weird, because I was sure I was doing this the correct way?!