public static class JIMSMessage
{
    public static bool Show(IEventAggregator _events, string message)
    {
        _events.Publish(new Message()
        {
            MessageValue = message
        });

        return true;
    }
}

JIMSMessage.Show(_events,"Enter Ledger Name.");

public ShellViewModel(IEventAggregator events)
{
    // Subscribe to MessageDisplayed events
    events.GetEvent<MessageDisplayedEvent>().Subscribe(HandleMessageDisplayed);
}

void HandleMessageDisplayed(MessageDisplayedEvent e)
{
    if (e.SomeBooleanProperty)
        // Do Work
}

// Broadcast an Event
_events.GetEvent<ShowMessageEvent>().Publish(
    new ShowMessageEvent{ Message = "Enter Ledger Name." });