I don't remember a reported example of that actually happening (though my memory could be the fault).

Certainly, since at least August 1943, the instructions printed on the back of US (and other) military mirrors have recommended sweeping the horizon in the hopes of this.

Sample instruction language:

• US military issued glass MIL-M-18371 mirrors (1950s to current day)
  
  "EVEN THOUGH NO AIRCRAFT OF SHIPS ARE IN SIGHT, CONTINUE SWEEPING THE HORIZON FOR MIRROR FLASHES MAY BE SEEN FOR MANY MILES, EVEN IN HAZY WEATHER."
• 
  French SOS-643 Military mirror (like American B-1 from 1945) Feb. 1954
  
  "Even though, no aircraft of ships are in sight continue sweepink [sic] the horizon. Mirror flashes may be seen 10 miles, away even in hazy weather."
• 
  BuAer Spec 23M5 (AER) ca. 1950
  
  EVEN THOUGH NO AIRCRAFT OF SHIPS ARE IN SIGHT, CONTINUE SWEEPING THE HORIZON. MIRROR FLASHES MAY BE SEEN FOR MANY MILES, EVEN IN HAZY WEATHER.
• 
  NAVY VERSION OF ESM/I : 11/1943:
  ESM/2
  B-I Red retroreflective aimer mirror, 1945:
  
  "PRACTICE SWEEPING HORIZON WITH AIMED BEAM EVEN IF NO RESCUER IS IN SIGHT, AS MIRROR HAS A RANGE UP TO TEN MILES."
• 
  GENERAL ELECTRIC ESM/I Double-sided mirror (cross-shaped aperture):
  PROTOTYPE: 8/1943: ( ALSO ARMY VERSION, SPEC 40654) 11/1943
  
  "WHEN RESCUE CRAFT ARE NOT VISIBLE, PRACTICE SWEEPING CROSS SHAPED SPOT ALONG THE HORIZON. FLASH MAY BE SEEN 10 MILES"