Attach a logic analyzer to the EPROM i/o of any of your Macs and check register 68000 which is initialized at the very beginning of the powering up cycle. As soone as your Mac does ANYTHING (like booting) the register is deleted again, but for this very short time, something very interesting is written in ASCII code into this register.
Also, there is a very nice weapon etched into the G3 processor. Impossible to see with the human eye, but a good microscope might do it.
Also, one of the registers initialized when the filesystem HFS is started contains also some interesting stuff from the programmers, initials etc.
there are SO many eastereggs on all levels of your mac (if you own a Mac Plus, open it and take a look at the inside and what's written onto the sides of the Mac