I wouldn't image it would be allowed?
Does it say on their website that you are able / allowed to do it?
Also, I think it's externally written to your site. You would have to edit the files on THEIR server to remove the text I would imagine.
HTML Code:
<script type='text/javascript'>
clicksor_default_url = '';
clicksor_layer_border_color = '#333333';
clicksor_layer_ad_bg = '#CCCCCC';
clicksor_layer_ad_link_color = '#666666';
clicksor_layer_ad_text_color = '#333333';
clicksor_text_link_bg = '';
clicksor_text_link_color = '#CCCCCC';
clicksor_enable_text_link = false;
durl = '';
clicksor_enable_pop = false;
clicksor_frequencyCap = -1;
clicksor_banner_border = '#999999';
clicksor_banner_ad_bg = '#CCCCCC';
clicksor_banner_link_color = '#666666';
clicksor_banner_text_color = '#999999';
</script>
<!-- I would imagine this bit here would be the part that stores the
information therefore you wouldn't be able to remove it locally -->
<script type='text/javascript'
src='http://ads.clicksor.com/showAd.php?pid=26677&sid=52933&adtype=10'></script>
<noscript>
<a href='http://www.clicksor.com'>Contextual advertising</a>
</noscript>