What Are The Most Likely Indicators Of Espionage?

What Are The Most Likely Indicators Of Espionage? Unexplained affluence, or life style inconsistent with known income. Notably, sudden purchase of high value items or unusually frequent personal travel, which appears to beyond known income. Sudden repayment of large debts or loans, indicating sudden reversal of financial difficulties. What are the elements of espionage? Contact/Communication.