You will not see SOLAS flares "flashing" high in the sky at a distance. You would see single bright lights. One for each flare launched. Maybe you would see light reflecting on a low cloud. You would not see "flashes". At night you should see RED for disaster.
https://www.youtube.com/watch?v=IEWN_y-3BY4The 12 gauge canister kits we see on most boats will do almost nothing. You would never be able to signal anyone over a hill with the 12 gauge kits. You may be able to get the attention of a passing boat but not much more. Any boat in open water should have fully approved SOLAS flares and signals; along with someone who knows how and when to use them.
http://www.westmarine.com/solas-flaresA proper maritime disaster flare is VERY distinctive. Everyone will stop, look, and notice.
For anyone with a plan to skipper or actively crew outside of Sir Francis Drake Channel or anywhere into open water. US Sailing Safety at Sea Seminar is a worthwhile activity.
http://www.ussailing.org/education/safety-at-sea/If you remember taking Red Cross Lifesaving as a kid. Safety at Sea would be a nautical intellectual equivalent for adults.
