I overlooked this rescue from May 22, 2018.

His hiking companion injured himself in the Grand Canyon,
and he used his PLB to summon help, but the helicopter
was having trouble spotting them. Per the PLB owner:

"The search and rescue team had a hard time spotting us from the air. I used a signal mirror and the pilot said thatís how they were able to locate us."

So - even if you have a PLB (and you should) the signal mirror is still a good idea!

Story here: https://www.acrartex.com/stories/tapeats-creek-arizona-usa
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A signal mirror should backup a radio distress signal, like a 406 MHz PLB (ACR PLB) (Ocean Signal PLB)