Read AVR / Atmega2560 signature byte area; signature is at addresses 0, 2, 4, calibration byte is at address 1

gistfile1.txt

#include <avr/boot.h>

void setup() {
  Serial.begin(115200);
  // put your setup code here, to run once:
  for (uint8_t i = 0; i < 16; ++i) {
    Serial.print(i);
    Serial.print(": ");
    Serial.println(boot_signature_byte_get(i), HEX);
  }
}

void loop() {
  // put your main code here, to run repeatedly:

}