The Hidden Preservation Marks are a network of preservation symbols embedded throughout the Archive during multiple construction and restoration periods. Examples have been documented beneath paint layers within observatory corridors and stitched into curtain linings and carved into support beams and incorporated into floor mosaics and pressed into book bindings and woven into carpets and concealed within decorative architectural features. Unlike primary preservation systems the marks operate as passive reinforcement structures intended to strengthen stability continuity and long-term resilience across the Archive. Historical analysis suggests successive generations of caretakers added new marks over centuries creating overlapping layers of protection designed to endure knowledge loss structural damage and caretaker succession. Their widespread distribution indicates deliberate integration into ordinary maintenance and construction practices rather than centralized installation. The marks remain active despite many examples having been concealed beneath later repairs and renovations.