SG 02 : A common symbol for specific gravity, sometimes appended to a measurement as if it were a unit, as in "1.134 SG" for a specific gravity of 1.134. (Specific gravity is a mathematical ratio of densities, so it has no unit.)
Russ Rowlett (Director), How Many? A Dictionary of Units of Measurement, Center for Mathematics and Science Education University of North Carolina, USA 2005. http://www.unc.edu/~rowlett/units/dictA.html, (Unit of Meas and Covr Factors - Amer) {608}