1. A fire intended for a signal.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• aignal fire,
• zignal fire,
• xignal fire,
• dignal fire,
• eignal fire,
• wignal fire,
• sugnal fire,
• sjgnal fire,
• skgnal fire,
• sognal fire,
• s9gnal fire,
• s8gnal fire,
• sifnal fire,
• sivnal fire,
• sibnal fire,
• sihnal fire,
• siynal fire,
• sitnal fire,
• sigbal fire,
• sigmal fire

The adjective form of "signal fire" would be "signal".

The plural form of the word "signal fire" is "signal fires"

The singular form of the word "signal fire" is "signal fire".