The ditloid "30 S L A T" stands for "30 seconds left on a timer." Ditloids are word puzzles where numbers and letters represent a phrase, and in this case, the letters correspond to the words in the phrase related to a countdown or time measurement.
4 S's in Assassin
14 Lines in the London Underground System
4 stations on a monopoly set? 4 Soldiers on a Match Stick
284 Tube Stations in London
I Saw Three Ships
seven spikes on the statue of liberties head
12 seconds on the buzzer
2 lenses in a standard pair of glasses
2 Little Dickie-Birds Sitting on a Wall (One Called Peter, One Called Paul)
19 a song by Paul Hardcastle
This is a Ditloid. The answer is 0 (zero) Sides on a Circle.
6 Stars in the Flag of Australia