what is this currency?

[Gokian]

When I interact with an outpost It brings up 4 currencies at the top right of my screen,
Pieces of eight, a skull and crossbones one, the round silver coin used to buy normal stuff in game and the premium currency (gold square shape). What is the skull and crossbones bronzy colour one used for?

[Dynasource]

They're Sovereigns!
By exchanging seasonal currencies (currently bars) with William Blackwood, you receive Sovereigns. You can use these to purchase new items (cosmetics) on the Black Market, as soon as they become available.

[Gokian]

Originally posted by Dynasource:

They're Sovereigns!
By exchanging seasonal currencies (currently bars) with William Blackwood, you receive Sovereigns. You can use these to purchase new items (cosmetics) on the Black Market, as soon as they become available.

Looking in game it's not the same currency, the exchange one is a skull, side on with a crown and octopus legs on it that is exchanged for bars. mine is just a round bronze coin with a skull and bones, typical pirate flag icon on it.

[the bat kite]

They keep adding and changing currencies all the time to keep you chasing that thing you "need." There have been about six currencies in year one. Then there are rare earth minerals as currency that come and go [when] in season (literally). The new one appears to be large chocolate bars! Seriously, they aren't made out of any valuable element found on Earth. It's stupid. I have 2.6 million silver coins but silver can't buy ♥♥♥♥. Because they have made the same old boss ships ridiculously bulletproof, able to take two hundred solid hits and still be healthy enough to drop a couple of mortars and kill your MAXED-OUT super ship, you now have to upgrade EACH weapon on your ship with some kind of "exotic materials modules" that cost about 5 chocolate bars per upgrade (there are three upgrade levels per weapon).