In this paper we propose an interactive system that allows only the owner of a target object to secretly find it among other similar or identical objects, which we call SecretSign. Finding a personal object, e.g., an assigned vehicle in a car-sharing parking lot, where there are many cars that look the same or are similar, can be difficult. In addition, we may not want to notify other people which object we are looking for, e.g., a car thief waiting to steal a car when the driver opens the door. Our proposed system allows a user to find an object without notifying others of the target, using a light attached to the target object which turns on and off in conjunction with user's operation of a remote control device, while lights on the other objects turn on and off randomly. We experimentally evaluated the system, in both virtual and real-world environments, and verified that SecretSign enabled users to quickly find their target objects without revealing the target to observers.