I'm not sure in which context you are using it, but based on this code (which works):
<%# IfEmpty(Eval("ArticleSummary"), "<h3>It's empty</h3>",Eval("ArticleSummary")) %>
you can try something like:
<%# IfEmpty(GetStringValue("Url", string.Empty) , "", "<span class=\"arrow\"></span>" + GetStringValue("Url")) %>
NOTE: I improvised second part for showing arrow, but you can put any html you want.
If the HTML is more complicated then simple one row change, you can add placeholder around it and try something like this:
<asp:PlaceHolder ID="ShowArrowIfLinkExist" runat="server" Visible=<%# IfEmpty(GetStringValue("Url", string.Empty) , false, true) %>>
<p> This is some example with <i class="arrow">arrow</i> in text.</p>
Hope this will help you.