is the squadron tail code, and the two digit numbers are used to identify the aircraft within the squadron. Each aircraft also carries a Bureau Number (usually shorted to BuNo) that acts as the serial number, and doesn't change if the aircraft is reassigned. The BuNo is a 6-digit number, and on the F-18 it is usually below the horizontal stabilizers.
Looking at the Scramble.nl database, it looks like you have:
-02 BuNo 165410 F/A-18D CN 1434/D141
-05 BuNo 165680 F/A-18D CN 1469/TAFD001 - this was one of eight Hornets ordered by the Royal Thai Air Force in the late 1990s. That deal was cancelled before the aircraft were delivered, and they were acquired by the USMC