Originally Posted By: hikermor
I'm hiking along and I see your parafoil. How do I know whether you are in distress or simply relaxing, enjoying the contrast of the colored parafoil against the blue sky?


It's not a sure thing, since the passersby might not be familiar with
46 CFR 160.072: DISTRESS SIGNAL FOR BOATS, ORANGE FLAG
https://www.uscg.mil/hq/cg5/cg5214/vds.asp#160.072
( Orange flag with black square above a black circle)

However, the Sky-Alert Parafoil Rescue Kite
http://www.landfallnavigation.com/-skite.html,
tries to answer that objection by conforming to that distress-flag pattern.

Originally Posted By: hikermor

For the same weight, wouldn't a PLB be much more effective? For less weight, how about a good whistle or a signal mirror?


I'm unclear on the weight of this item, and I agree about the PLB and other items. One other claim made for this is that it will loft a strobe, which could be handy in the appropriate circumstances.
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A signal mirror should backup a radio distress signal, like a 406 MHz PLB (ACR PLB) (Ocean Signal PLB)