In recent years, the use of drones for recreational and commercial activities has grown rapidly due to their affordability and performance. This growing use raises concerns about the threats drones pose to the security of sensitive areas such as airports, prisons, industrial and military facilities. In response to these threats, drones detection methods are being actively developed. In particular, most camera-based methods rely on appearance to perform detection. They are therefore prone to error due to the great similarity between drones and some other flying entities such as birds. However, from a kinematic perspective, unlike birds, drones, especially multicopters, have a propeller rotation speed. The method proposed in this paper uses the propeller rotation speed as the key physical parameter on which to rely to unambiguously distinguish drones from other flying entities. The basic idea consists in using discrete Fourier transform to determine the propellers rotation speed from high frame rate videos, and extracting the propellers induced drone signature as a quantitative camera-based drone signature. The proposed algorithm proceeds as follows: flying entities are continuously tracked in the sky; discrete Fourier transform, applied to the video stream within a time window ending at the current instant (frame), is used to extract the propellers induced drone signature which unambiguously confirm each flying entity as being a drone or not. Experimental results obtained using a consumer-grade camera at a frame rate of 240Hz demonstrate the effectiveness and reliability of the proposed method.