The parking stickers are now awarded per physical person, and no more per household, as it was previously the case. The number of parking stickers per person is now limited to 3.
Getting a 4th sticker is now outlawed.
In addition, the inclusion of several vehicles by sticker is also banned. Only one vehicle can be attributed to one parking sticker.
As a reminder
The parking sticker is reserved for the inhabitants of the Luxembourgian capital and allows them to park for free and without any limitation of time in their district of residence. These stickers must be placed on the windshield of the vehicle, so as to be clearly visible from the outside. Parking stickers come in 3 different types : annual, provisional (valid for 20 days) or visitor (valid for 3 months at a cost of 16 euros) stickers.
The city of Luxembourg clarifies that "The residential parking sticker is optional. The application to get it must contain, in addition to a residence certificate, a registration card prepared on behalf of the applicant.”
Moreover, if the first sticker is free, the application for one or more other parking sticker(s) implies the payment of a fee.
More info the City of Luxembourg web site.