AT 0954:54, PLT OF PIPER PA-32RT, N39614, RPRTD 9 MI NORTH FOR LNDG. TWR CONTROLLER (NORTH CTLR) TOLD HIM TO PLN FOR A RGT ENTRY TO RWY 27R. AT 0955:32, A STUDENT PLT & INSTRUCTOR (CFI) IN CESSNA 172N, N75584, WERE CLRD FOR TKOF ON RWY 33 WITH A 'RIGHT TURN OUT' IAW NOISE ABATEMENT PROCEDURES. APRX 2 MIN LATER, THE PA-32 PLT RPRTD TURNING DOWNWIND OVER A PROMINENT LND MARK. THE TWR CTLR REPLIED THAT THE PA-32 WAS 'NOT IN SIGHT' & CLRD THE PLT TO LND ON RWY 27R. NO FURTHER X-MISSIONS WERE RCVD FM EITHER ACFT. THE 2 ACFT COLLIDED NRLY HEAD-ON AT ABOUT 1000' MSL, APRX 1 MI NORTH OF THE DEP ENDOF RWY 33. THE CESSNA CRASHED INTO A PG&E FACILITY & BURNED; A SECURITY GUARD WAS INJURED THERE. THE PA-32 CRASHED IN A NRBY BAY. INV REVEALED TWR PSNL HAD NOT PROVIDED TRAFFIC ADZY TO EITHER ACFT & THAT THE BRITE RADAR WAS OUT-OF-SVC FOR ROUTINE MAINT. ARPT PSNL HAD POSTED SIGNS ARND THE ARPT WITH NOISE ABATEMENT PROCEDURES W/O FAA APVL, WHICH EFFECTIVELY RDCD SEPN BTN DEPG/ARRG ACFT. FAA TFC MGR DID NOT ORDER MODIFICATION OR RMVL OF SIGNS WHEN HE LEARNED OF THEIR PRESENCE.