Вы хотите использовать Android.App.Notification и Android.App.NotificationManager , например, из LocalService.ShowNotification () :
// within some Android.Content.Context subclass (Activity, Service, etc.)
void ShowNotification ()
{
IEnumerable<char> text = GetText (Resource.String.local_service_started);
var notification = new Notification (Resource.Drawable.stat_sample,
text,
System.Environment.TickCount);
PendingIntent contentIntent = PendingIntent.GetActivity (this, 0,
new Intent (this, typeof (LocalServiceActivities.Controller)),
0);
notification.SetLatestEventInfo (this,
GetText (Resource.@string.local_service_label),
text,
contentIntent);
var nm = (NotificationManager) GetSystemService (NotificationService);
nm.Notify (Resource.String.local_service_started, notification);
}