Dell Inspiron 15R (N5110, Early 2011) - Manual (Page 68)

68 System Board
18 Enter the service tag (see "Entering the Service Tag in the BIOS" on
page 68).
Entering the Service Tag in the BIOS
1 Ensure that the AC adapter is plugged in and that the main battery is
installed properly.
2 Turn on the computer.
3 Press <F2> during POST to enter the system setup program.
4 Navigate to the security tab and enter the service tag in the Set Service Tag
field.