The importance of authentication is paramount when it comes to the protection of resources, encompassing both physical corporate facilities and digital assets. Among the different authentication methodologies, 3D on-air signatures represent a novel behavioral biometric that is highly challenging to imitate, even when observed from a distance. However, the emergence of robotic arms capable of mimicking human movements poses a potential security vulnerability for these emerging schemes. This paper focuses on examining the possibility of generating 3D fingertip movements that accurately mimic a signature, with the intention of circumventing a biometric system. We utilize the iDeLog3D algorithm to produce artificial movements of the fingertips, based on the 3D Sigma-Lognormal model and the Kinematic Theory of Rapid Movements. We then replicate a 3D on-air database using this model and proceed to compare the performance of a DTW-based signature verifier using both real and synthetic signatures. During the experiments, it has been demonstrated that synthetic signatures are effective in bypassing a signature verifier that is exclusively trained using real signatures. This underscores the importance of incorporating an additional layer of security, such as a bot detector, into these types of biometric schemes.