Just flew Cityflyer SYDMEL on a 738. At boarding, the agents had some specially printed red luggage labels with them that stated something like "This item must be stored underneath the seat in front of you.", and by implication, not in the overhead lockers. Perhaps I've missed them previously, but this was the first time I've noticed this. I didn't get to see them using these tags for any pax's items, so am wondering what is behind this?, and what kind of item are they trying to exclude from the overhead lockers? Has this been a regular part of domestic boarding procedure for any length of time?