Fingers crossed it's for a sports car of some description.
For understandable reasons, carmakers like to keep their development projects under wraps for as long as possible. For sure, you're always going to have leaks and spy photographers to contend with, but cars like the 1955 Paris Show-stealing Citroen DS and the Ford GT from the 2015 NAIAS are proof that a vehicle can be hidden from the press and public right up to its unveiling. And it looks like Honda came so close to shrouding from us whatever it's just been spotted filing a new trademark of 'ZSX' for.
Obviously, there's only so much you can deduce from a trademark filing, and even less when the request is made in a territory that a company is already active in. However, educated assumptions can be made to hopefully identify what the 'ZSX' actually is. As the trademark was filed in the European Union, we can deduce that whatever vehicle the ZSX tag will be applied to is going to be sold across other major territories (for instance, the launch of the 2017MY Civic hatchback in the States should mean every Honda sold in the EU will have a Honda or Acura equivalent in the US), and the NSX-esque naming structure implies this name will be brandished on a sportier model of some description.
A quick perusal through our Honda news archives does indeed reveal reports on two sports car projects that the company is working on: one with more conventional gasoline tech, and the other being a pure EV. Regarding the latter, the 'Z' in the 'ZSX' name could be a subtle hint at a zero-emissions car. Of course, there's no substance to that claim, but Honda does have a habit of applying genuine meaning to its acronym names - remember how the NSX was supposed to stand for 'New Sportscar eXperimental'? So, if Honda does end up revealing an all-electric performance model with a name that means 'Zero-emission Sportscar eXperimental', you read it here first.