O.K. this is a trick posting, because, as far as I know, JBL's first product, the D 101 speaker was never given serial numbers.
The D 101 (D101, D-101) had the model number cast into the frame and initially bore the "Iconic" label, badge or name plate, the first one shown below.
A second version of the Iconic label added the "Trade Mark Reg." under the three stars on the upper half. Maybe this was what prompted Altec to apply enough pressure to cause Jim Lansing to stop using the "Iconic" name.
The final D101s appeared with the rectangular logo adopted when JBL move to the Marquardt facility in Venice, Ca. in late 1947 (more details here: http://audioheritage.org/html/histor...g/founding.htm )
The first D130, D175 and N1000 components and D-1000 cabinet also bore this rectangular decal and no serial numbers, but I haven't seen it used on any other models.