We give a general test to certify that the quantum phenomenology in the linear response regime cannot be described by any noncontextual emulator. This allows us to provide the first proof of a quantum signature in the power output of a quantum engine certified against generic classical emulations -- a necessary milestone to prove the conjectured superiority of quantum thermal machines over classical ones. Given the ubiquity of linear response theory, we anticipate that our tools will allow to certify the absence of classical emulators for a wide array of quantum phenomena.

The talk will be based on paper arxiv:2004.01213.