The Full Form of BOLO is‍ Be on the lookout.

: to watch or search for (something or someone) : be alert toBe on the lookout for flooded roads after heavy rainstorms.

The police officer walked through the neighborhood, keeping a (sharp) lookout for any suspicious activity.

be on the lookout for somebody/something
• From February to July he was on the lookout for blossoms.
• Naturally, he was on the lookout for more exciting activity.
• But Henry was not feeling like defending anyone today, rather he was on the lookout for attack.
• Please be on the lookout for talent in your classes and give serious consideration to auditioning yourself.
• When we find that, we should be on the lookout for some ever-changing enemy, some arms-race rival.
• I told Thompson to alert all the guards on duty to be on the lookout for a small brown rodent.
• Police are also asking people to be on the lookout for bogus officials following several incidents in the area.
• Still, they will be on the lookout for opportunities to let members know about their achievements whenever appropriate.