This invention is directed to security features that are formed, created, printed from inks comprising metallic particles and/or metallic nanoparticles. Preferably, the security feature is a reflective security features that comprises metallic nanoparticles where the reflective security features are formed by a direct-writing process, e.g., an ink jet printing process, using an ink comprising metallic nanoparticles. The invention is also directed to the use of these security features in many applications and to processes for making them.