<asp:Panel id="tags" runat="server" DataSource="<%# this.DataSource %>">
    <asp:Repeater ID="rptTags" runat="server">
        <ItemTemplate>
            <span class="tag"><%# Eval("Name") %></span>
        </ItemTemplate>
    </asp:Repeater>
</asp:Panel>

if (rptTags.Items.Count == 0)
    {
        tags.Visible = false;
    }

<asp:Panel id="tags" runat="server" Visible="<%# ((IEnumerable)DataSource).LengthOrSomething %>">