HtmlHelperExtension.cs

public static HtmlString RenderPersonalizationRuleHightlight<T>(this HtmlHelper<T> htmlHelper)
{
    var result = new MvcHtmlString(string.Empty); 
    if (!Sitecore.Context.PageMode.IsExperienceEditor)
    {
        return result;
    }

    var sitecore = htmlHelper.Sitecore();

    if (sitecore.CurrentRendering == null || sitecore.CurrentRendering.Properties == null)
    {
        return result;
    }

    string rulesString = sitecore.CurrentRendering.Properties["PersonlizationRules"];

    if (string.IsNullOrEmpty(rulesString))
    {
        return result;
    }

    try
    {
        var rules = XElement.Parse(rulesString);
        var elements = rules.Descendants().Elements("rule").ToList();
        if (elements.Count() > 1 || elements.Any(e => e.Attribute("uid").Value != ID.Null.ToString()))
        {
            result = new MvcHtmlString("<div class='page-editor-dach-highlight'>This rendering uses personalization rules.</div>");
        }
    }
    catch (Exception e)
    {
        Sitecore.Diagnostics.Log.Error("An error occured: ", e, typeof(HtmlHelperExtension));
    }

    return result;
}