Unique identification of controllers

I have 20 AX1500's with encoder modules on order from your company, and I need to be able to uniquely identify them through the RS232 port. Is there any way to read the serial number from the board, or store a number in an empty parameter or anything like that? I read in the manual that you can read the encoder ID from the board, is that a unique number?

There are a few EEPROM areas that you could use for that purpose.
use the command ^FA xx (cr) to write a byte (where xx is your value). To read just send ^FA (cr)
Before you write anything, read and verify that it contains $FF.