This document describes common methods for locating serial-numbers for the Email Security Appliance (ESA), Security Management Appliance (SMA), and Web Security Appliance (WSA).
From the GUI
For the ESA and WSA, you will navigate to Monitor/Reporting > System Status
For the SMA, you will navigate to Centralized Services > System Status
From the CLI
You will use the version command.
Current Version =============== Product: Cisco C100V Email Security Virtual Appliance Model: C100V Version: 13.0.0-392 Build Date: 2020-01-29 Install Date: 2020-04-28 04:01:27 Serial #: 564D31FC43F2BDD28977-898C3195F3F4
Physical Access (Hardware)
For hardware models (x70, x70, x80, x90, x95, etc) you will see a sticker on the rear-panel containing the serial number. In some cases on newer models, you will see a pull-tab on the front-panel which should also show the serial number.