According to Motorsport Italy, Ferrari adjusted the mirrors to prevent them from being labelled as 'illegal' during the Azerbaijan Grand Prix. This was done after teams complained to the FIA that they believe the rules were not being observed at the Scuderia outfit.
From the top view of the car, no bodywork should be seen between the sidepod and edge of the floor. This was not the case at Ferrari. So they decided to put three teeth at the top of the mirrors in Baku to be compliant with the mirror regulations.
The innovative Ferrari mirrors ensure that airflow is better for the SF71-H. Mercedes and Red Bull use similar mirrors, but with them, the asphalt was visible and thus complied with Article 3.5.5. For technical photos and more explanation see the Motorsport.com site. (Photo: Ferrari Media)