The HIN (Huul ID Number) is molded into the transom, usually near the starboard side within 2" of the rub-rail. It is also marked in at least one other location hidden inside the boat. However, it SHOULD be noted on your registration or Documentation paperwork and title.
The format is XDYFccccmyxx, where XDY = O'DAY (might be "STR" if boat was built during the short time that O'DAY was part of Starcraft Sailboats, Division of Lear Siegler), F = 272, cccc = Sail or Class# (that is most likely the number you seek), m = code for month of build (A = January, B = February, etc), y = last digit of year of build, xx = last 2 digits of Model Year.
Having said that, though.... unless you are racing "One-Design" (that is strictly against other 272s), you really want/need a number from the US Sailing Association. Other owners (not just 272 owners) who race will know how to obtain that information.