You can create a custom macro method with something like this in it

public string GetSiteSetting(string settingKey)
{
return SettingsKeyProvider.GetStringValue(CMSContext.CurrentSiteName + "." + settingKey)
}

I don't know if there are any built in macro methods for this, but I don't think there are.

If you don't know how to add custom macro methods, look in /app_code/samples/classes/custommacromethods.cs for an example and /app_code/samples/modules/samplemacromodule.cs to see how to load them.

I find the custom macro methods to be extremely useful.

Here is what you can put in the CustomMacroMethods.cs file

Put this in the RegisterMethods() Block:

        MacroMethods.RegisterMethod("GetSiteSetting", GetSiteSetting, typeof(string), "returns value of site setting with specified setting key", null, 1, new object[,] { { "type", typeof(string), "The settings key name. " }, { "siteName", typeof(string), "The site name. If this parameter is omitted, the value of CMSContext.CurrentSiteName will be used" } }, null);

add these methods to the class

 public static string GetSiteSetting(string settingKey, string siteName)
    {
        return SettingsKeyProvider.GetStringValue(String.Format("{0}.{1}", siteName, settingKey));
    }
    public static object GetSiteSetting(params object[] parameters)
    {
        switch (parameters.Length)
        {
            case 1:
                return GetSiteSetting(ValidationHelper.GetString(parameters[0], String.Empty), CMSContext.CurrentSiteName);
            case 2:
                return GetSiteSetting(ValidationHelper.GetString(parameters[0], String.Empty), ValidationHelper.GetString(parameters[1], String.Empty));
            default:
                break;
        }
        return null;

    }