Sigma

Sigma is a Planet in the Faction Wars Update of SAS4. It is an Oceanic planet, and the only source for Sigma Credits. Zombies living on Sigma are reported to be healthier than usual, having 20% Extra attack power and 15% Health, most probably because they receive proper Hydration and Nutrient-Rich Prey.

Faction Warfare Items
You can buy the following Faction Warfare items with Sigma Tokens:

Kraken

Depth Charge

Mako Helmet

Mako Vest

Mako Gloves

Mako Pants

Mako Boots

Trivia

 * The fact that the Mako Series is only buyable with Sigma Credits is because the Mako Set is built for underwater explore, and Sigma is an Oceanic Planet, so underwater explorers living on Sigma may have used it for their exploration.
 * Additionally, Planet Sigma is named from Greek letter Sigma (Σ/σ/ς) . In general mathematics, Σ is regularly used as the operator for summation. This could be referred to Physics theory about total pressure applied on an object being in the water. This further explains that Mako Series is well-built to withstand high-pressure as wearers are under water.