XF 1.5 Notice on first page of threads list

There wouldn't be a condition that would do this for a notice. You could potentially do this with a direct template edit and conditionals, though it won't work like a true notice (dismissability, display, etc).

 

Like Mike said, a template edit can be used. It's crude but it works:

Admin CP -> Appearance -> Templates -> PAGE_CONTAINER

Add the red code:

Code:

			<xen:if is="{$sidebar}">
				<div class="mainContainer">
					<div class="mainContent"></xen:if>
						
						<xen:include template="ad_above_top_breadcrumb" />
						
						<xen:if is="{$requestPaths.requestUri} == '/index.php?forums/main-forum.2/'">
							<p class="importantMessage">
								THIS MESSAGE WILL SHOW AT THE SPECIFIED URI
							</p>
						</xen:if>
						
						<xen:hook name="page_container_breadcrumb_top">
						<div class="breadBoxTop {xen:if $topctrl, withTopCtrl}">
							<xen:if is="{$topctrl}"><div class="topCtrl">{xen:raw $topctrl}</div></xen:if>
							<xen:include template="breadcrumb"><xen:set var="$microdata">1</xen:set></xen:include>
						</div>
						</xen:hook>
						
						<xen:include template="ad_below_top_breadcrumb" />
[/color]

If you use friendly URLs then it won't have the index.php part.