2
You will need to edit the main menu template to do this, then adjust your style.css for the additional class -
<table cellspacing="0">
<tr>
<td id="mainmenu">
<a class="menuTop[color=ff0000]<{if $xoops_dirname=='system'}> actlink<{/if}>[/color]" href="<{$xoops_url}>/"><{$block.lang_home}>a>
<{foreach item=module from=$block.modules}>
<a class="menuMain[color=ff0000]<{if $xoops_dirname==$module.directory}> actlink<{/if}>[/color]" href="<{$xoops_url}>/modules/<{$module.directory}>/"><{$module.name}>a>
<{foreach item=sublink from=$module.sublinks}>
<a class="menuSub" href="<{$sublink.url}>"><{$sublink.name}>a>
<{/foreach}>
<{/foreach}>
td>
tr>
table>
and in style.css -
.actlink {border-right: solid #0a1b51; background-color: #dde;}
In your case, the stylesheet would specify an image for the .actlink class
