F-Zero and Star Fox trademarks have been filed by Nintendo, potentially pointing towards future plans for the two franchises. Though the trademarks haven't indicated whether or not Nintendo is working on brand new games in either series, this will at least be hopeful news to those hoping to see the return of Fox McCloud and Captain Falcon.
Star Fox has received a relatively recent mainline release in the form of Star Fox Zero, which received a modest critical reception though failed to set the sales charts alight. On the other hand, F-Zero has been more-or-less completely overlooked by Nintendo, outside of its appearance as a mini-game in the Wii U's Nintendo Land.
With Nintendo fans having requested a brand new F-Zero game since the days of the Gamecube, it is hoped that this trademark could point towards a sequel in the future. Other trademarks filed by Nintendo (via Reset Era) include Pikmin, Nintendogs, and Sin and Punishment.
Earlier today, a rumored leak suggested that Nintendo was working on Star Fox Grand Prix, a Star Fox racing game. The leak featured a logo reportedly taken from the upcoming game. Nintendo has maintained a radio silence regarding the future of F-Zero, though with the Switch's focus on multiplayer it could possibly make a comeback sooner rather than later.
E3 2018 will likely see Nintendo clearing the air regarding these rumors (don't forget to make your E3 predictions here), and it's entirely possible that it is filing these trademarks for projects outside of brand new games. However, this is unlikely to prevent Star Fox and F-Zero fans from crossing all their fingers and desperately hoping for brand new releases.