12 S of Z represents 12 Signs of the Zodiac.
It is similar to the
1. 52 W in a Y - 52 weeks in a year
2. 3 H in a C - 3 Hands in a Clock
3. 3600 S in an H - 3600 Seconds in an Hour
4. 5 O in the W - 5 Oceans in the World