Mark 4 energy level was a measure of energy used as reference by members of the Aegis, indicating an advanced level of technology.
History and specifics[]
In the year 1968, Gary Seven discovered technology being used by a Soviet spy ring utilizing energy levels at mark 4, "hundred of years ahead" of 20th century Earth. (TOS - Assignment: Earth comic: "Brighter Than a Thousand Suns")
Seven later discovered this technology had been provided by the group Counter Strike. (TOS - Assignment: Earth comic: "We Have Met the Enemy...")