If you need help from a helicopter in the backcountry, do not wave with one arm—pilots interpret this as "hello." Instead, always signal a 'V' or a 'Y' with both arms. If you do not need help signal an 'N,' which is one arm up, the other down; an 'X' with your arms means 'need medical aid/assistance.' Review the International Civil Aviation Organization (ICAO)'s appendix in their manual International Standards And Recommended Practices For Search and Rescue.