This may help...
http://www.dtic.mil/dtic/tr/fulltext/u2/a081153.pdf

From 1980 a US military critical evaluation of survival kits and vests they use. It gives statistics how pilots were rescued, what items in the survival kit were used. Table 2 "Means used to Locate Individual" on page 11 ranks mirror 15th out of 28. I'm still going to pack a mirror anyway.