DDan is correct.
Alternatively, you can hit the menu button (lower side button on scanner)
Scroll down (using the knob on top) to "Search for" Hit the Eyes key on the lower right front of the scanner.
Scroll down to "Edit Service". Hit the Eyes key.
Public Service is the first band in the Service Search section and it should already be hi-lited. Hit the Eyes key again.
Scroll to "Search with Scan" and hit Eyes.
Scroll to "Set Lockout" and hit Eyes
Scroll to "lockout" and hit Eyes to permanently lock the system out or Temporary L/O if you want it start up again as soon as you turn the scanner on next time.
This procedure works the same for all the Service Search banks and is similar for any Custom Search banks you put in.
Happy scanning,