FLC OF MLG DEPARTING BWI MADE TURN AT 300 PER SID. FLT HAD NOT BEEN CLRED ON SID BUT HAD BEEN CLRED RWY HDG.

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AS A BALTIMORE BASED AIRLINE CREW; THE CAPT AND I HAD FLOWN MANY DEPS AND ARRS OUT OF THE BWI ARPT. WE WERE BOTH UNDER THE IMPRESSION THAT THE AUTOMATIC TURN TO HDG 150 DEGS AT BAL VOR DME 3 NM FOR RWY 28 DEPS APPLIED TO ALL TURBOJET DEPS. OUR INITIAL CLRNC LIMIT ALT WAS TO 4000 FT. UPON CHKING IN WITH DEP CTL; WE WERE GIVEN CLB CLRNC TO 17000 FT. AT 3 DME ON RWY HDG WE INITIATED THE ABOVE DESCRIBED TURN TO 150 DEGS. AS WE WERE TURNING L THROUGH 210 DEGS; WE WERE QUERIED BY DEP AND GIVEN AN IMMEDIATE R TURN BACK TO 310 DEGS AND A 'STOP CLB' AT 5000 FT. COMPLYING WITH THE ALT WAS NO PROBLEM AS WE WERE JUST PASSING 4000 FT. WE WERE ADVISED THAT ONLY THE 'PALEO' AND 'SWANN' SIDS FEATURED THIS TURN AND THAT WE WERE EXPECTED TO MAINTAIN RWY HDG (282 DEGS) ON DEP. THE SOURCE OF DEP CLRNC WAS THE ACARS PDC DOWNLINK. UPON CHKING; WE VERIFIED THAT IT INDEED SAID 'FLY RWY HDG VECTORS ASSIGNED RTE/FIX;' AND NO SID HAD BEEN ISSUED. AT THE TIME OF THE INCIDENT THERE WERE NO OTHER ACFT IN OUR IMMEDIATE VICINITY AND OUR TCASII ISSUED NO TA. THE TURN/ALT CHANGE WERE MADE. I ASSUME; TO KEEP US WITHIN CTLR'S AIRSPACE. SUGGESTIONS: MAKE UP A 'BALTIMORE 1' SID THAT FEATURES RADAR VECTORS TO THAT EVERY DEPARTING ACFT IS ISSUED A SID. MOVE THE TKOF/DEP INSTRUCTIONS ON THE ACARS PDC TO PAGE 1 WHERE IT IS MORE LOGICAL; PROMINENT AND LIKELY TO BE NOTICED RATHER THAN ON PAGE 2 AT THE END OF THE SEQUENCE.