Look at the headbadge on the front of the bicycle. There should be a 4 digit number stamped into it. It can sometimes be difficult to see, but it should be there. The format is XXXY, where XXX is the day of the year, and Y is the year. For example, 1679 would be the 167th day of either 1979 or 1989. The decade should be pretty clear just from looking at the bicycle and its graphics. Can you post a picture?