<p>Unmanned aerial vehicles (UAVs), also known as drones, have become increasingly important in modern times due to their ability to perform a wide range of tasks in both civilian and military sectors. However, the resource-constrained nature of UAVs, along with the need for secure data transmission, poses considerable challenges for cryptographic implementations. To address these challenges, lightweight cryptographic solutions have been proposed over the last several years to meet the unique demands of UAV networks. One such solution is called signcryption, which combines encryption and digital signatures into a single step, offering the most suitable cryptographic solution for UAV security. This comparative review article analyzes the most up-to-date signcryption mechanisms, particularly those proposed for UAVs, by comparing their various cryptographic methods and identifying the most suitable one. With this article, we also aim to explore the key security requirements and challenges that a typical UAV usually experiences. The key findings are then presented, and potential research directions are identified.</p>