For a visual signal:
* Beacon: This is a very old word, referring to a fire or light used for signaling.
* Torch: This is another ancient term for a burning light, often used for signaling.
* Banner: This signifies a flag or cloth used to send messages visually.
* Standard: This is a flag, often associated with a leader or military unit.
For an audible signal:
* Clamor: This refers to a loud, confused noise, suggesting urgency.
* Trumpet: This is an instrument used for signaling, especially in a military context.
* Horn: This can refer to a variety of instruments used for signaling, often with a loud, piercing sound.
* Bell: This is an old word, but might not be considered "archaic" as it's still in use today.
For a general alarm or signal:
* Warning: This word signifies a call to attention or preparation for something dangerous.
* Foreboding: This emphasizes a sense of dread or apprehension about an impending event.
* Premonition: This suggests a feeling that something bad is going to happen.
The best choice for your specific situation will depend on the era, the tone, and the type of signal you're describing.