Heart Pirates

The Heart Pirates are an infamous and notable rookie pirate crew discovered on the Sabaody Archipelago around the time the Straw Hat Pirates arrived there. Their potential is further seen with the release of Haki by Silvers Rayleigh, upon which nearly every notable crewmate save one were not affected.

Pirate Flag
Like many other pirates from the North Blue, the Heart Pirates do not use a skull and crossbones, but a smiley instead, possibly symbolizing the "Age of Dreams".

Known Crewmembers
The most prominent feature of the crew is that they are all wearing the same boiler-suit, other than Law himself. The same boiler-suit have also been seen worn by the Tenryuubito and their slaves, with the only difference being that the Heart Pirates have their Jolly Roger on their suits. It appears they have at least 5 members.

Crew Strength
The crew was able to withstand a blast of Haki from Silvers Rayleigh.

It can be presumed that they are very strong for them to have made it all the way to Sabaody Archipelago. With the addition of the new member, famous pirate captain Jean Bart, the crew may have grown even stronger.

Trivia

 * Amongst all the Supernova Crews, next to the Straw Hat Pirates, the Heart Pirates is the crew with the most known members (although most of the other Supernovas appear to have more pirates in their crews if including unnamed members.)
 * Law's Jolly Roger bears some similarities with Doflamingo and Bellamy's Jolly Rogers, although one should note that Doflamingo and Bellamy's Jolly Rogers have a cross over them.