There are several synonyms for the phrase "in safe custody". These include terms such as secured, protected, guarded, and kept safe. "Secured" implies that the item or person is safely locked away or protected from harm. "Protected" suggests that measures have been taken to prevent any damage from occurring. "Guarded" means that something is being watched over and protected from potential threats. Similarly, "kept safe" indicates that an item or person is being carefully monitored and protected from any harm that may come their way. Regardless of the synonym used, each implies a sense of safety and security.