Just then I had a Skype chat with someone I found through one of those languages learning sites (and OMG thank God he was a good chat partner. They are so rare to find) and then he typed it "dorénavant" and immediately I made the connection that that was the word they were saying over the loudspeaker!
Here is the exact sentence : "Nous vous rappelons que dorénavant l'étiquettage de vos bagages est obligatoire." (We remind you that from now on it is compulsory to tag your luggage (with your details))
Now I only came across the word désormais because of Facebook (I had since switched my language to French about a year ago) but did not realise that dorénavant means practically the same thing ("from now on").
It's funny the different ways by which I learn new vocabulary!
Here is a somewhat related blogpost about train platform messages.