From SA Mafia Wiki
A Fakeclaim is just that: a fake roleclaim. Fakeclaims are a common tool to scum, who during a mass claim cannot come forth and say that they're scum. Fakeclaims can either be made up by the scum, or given to them by the mod.
The most common fakeclaims are miller, bulletproof, and vanilla. Scum will often be truthful in their role, if they're a power role, but lie about their alignment and potentially who they targeted with said role.
Generally, if you are a mod running a game with lots of flavor, you have an obligation to provide fakeclaims for your scum so they can avoid being the victims of flavor arguments.