Historical clue formulations

• Spreads outward — 2017-05-04
• Distress signals — 2012-08-15
• Burning emergency signals — 2011-10-17
• Some pyrotechnics — 2008-11-01
• Emergency lights — 2008-10-23
• Warning lights — 2001-12-27
• Some warnings — 1999-07-24
• SOS lights — 1998-03-30