I have had lots of KLM crew use the phrase mentioned above and it came across as very professional and friendly. I have adopted this approach when travelling with other carriers. I don't normally say at the boarding door as it's so hectic but will mention to one of the crew in the aisle.
The airline I work for, in a premeditated emergency, will ask for people with aircraft / military / medical experience to make themselves known and obviously, at this point, would greatly appreciate your assistance
You maybe met with a blank stare or a "so what" look by some, however others will pop an extra drink on your tray or whatever to acknowledge a fellow flyer.