Blue Light Special

What does the idiom “Blue Light Special” mean?

Definition:

1. a temporary sale at a discount store. 2. a traffic stop by the police.

For example:

“1. Come quick! The local discount store is having a blue light special—shirts are three for $10 until 10 p.m. 2. Sorry I’m late getting home—I was speeding, and I got the blue light special.”

Notes:

Both these expressions are less common now than formerly.