Military Letter Codes Novels & Stories

I asked and Alaric's gaze narrowed too, like he understood what she meant. "It's an ancient language," Alaric said. "Codes ancient kings used in war to pass orders secretly. It's mentioned in our private royal lessons but no one knows exactly what it looks like." He turned to his mother. "But you do, Mum." It sounded more like a question than a statement. "I only recognize it. I don't know what it means," she said. My interest piqued, If she could recognize the letters maybe we were closer to knowing what it meant.