Don't be discouraged One Off Contributor. It is the nature of pilots to rip apart any idea before really considering it's relative merits etc.
You have a sound suggestion. Take it a step further. Having implemented a random callsign/paint scheme, what other ways could a terrorist identify a target on his airband radio. Accent? Departure gate? Terminal?
There are always ways and means. Just watch Ocean's Twelve!
Keep the ideas coming though. That's what we need.
Regards.