PBO

Philippine Board of Orthodontics
Found on http://www.encyclo.co.uk/local/20895

PbO

Lead(II) Oxide Molar mass: 223.1994
Found on http://www.convertunits.com/molarmass/Lead(II)+Oxide

PBO

Permanent Beat Officers
Found on http://www.met.police.uk/foi/glossary.htm
No exact match found