While not exactly what you are looking for, there is a field available to use for a secondary identification.  From the serialized editing window, right click on the grid and and select "Window Customization - Choose Grid Fields".  Add the "Stock Number" column to the window.  Then right click again and choose the "Save Window Settings" under the same popup menu.  This field is simply a text entry field and does NOT enforce uniqueness like the serial number column, but you can enter in the plate number into that field and store it with the serial number.

Dear Terry, thanks for suggestion. Because i have already thousands of serials to associate, is there a way to import them instead of typing one by one?

Yes, you can import serial numbers from the "Options - Import" menu.