Sigma Serial Numbers do not provide an indicator of the year in which a particular model was built. However, most Sigma models were offered only for a limited number of years, so that most models' construction dates can be narrowed down to a reasonable range.
UsedPrice.com maintains a data base of market prices for used instruments, which is used as a reference source by retail dealers, insurance companies, manufacturers, libraries, pawnbrokers, etc. The construction dates and other data may not be completely accurate but they provide a general sense of when particular models were offered.
If you want to know how much your Sigma guitar is worth, you may click HERE to reach their web site, where for $3.99 you can obtain an estimate of the current value for your instrument.
Please note that the inclusion of this link in this site should not be interpreted as an endorsement by Sigma Instruments or by its parent, C.F. Martin & Co.