Finding serial no

BigIP 10.x version

Serial no. format f5-xxxx-xxxx

Command line
Login into console (advanced shell)
tmsh show sys hardware | grep -i chassis

Output will look like:
Chassis Serial f5-xxxx-xxxx

(or)
b platform | grep -i serial

Output will look like:
Chassis   serial f5-xxxx-xxxx


GUI
System -> Configuration -> Chassis Serial Number