[R-390] R390 Number Stamp Under ID Plate

[thoyer]

Working on R390 S/N 334. Tonight's project was to clean up the front panel.
It is in pretty good shape except where it looks like someone used a sharp
object to scrape off a label under the ID Plate so there are several
scratches there. Maybe one day I'll repaint the panel, but not right now.
 
Question for tonight is.... When I removed the ID plate stamped under it in
black ink is 347. What, if any, significance is this stamped number?
 
Tom
W3TA