Well the AIM doesn't offer a whole lot of guidance here but from the other side of window having done an ATC minor the callsign is the most important, the fact that you are IFR is very helpful but if you are an airliner it's pretty easy to assume that you are IFR so that goes without saying, and lastly the destination to verify that this is the correct flight plan. So callsign and destination are the important parts and if you are not flying an airliner it will definitly help to add the fact that you are IFR, in other words do I need to find a strip or make one? All you need. Frankly I think it's just a moot point. Who cares?