What this is supposed to be, I can't say exactly - but I think this represents what benefits your guild provides for this guild battle.

Yes, that's exactly right. In this example, it means your guild has the ability to use Gladiator cards in the battle and has the +1 mana benefit.

These new features for Brawl battles should make them feel quite unique and different from regular tournaments & ranked play. It's going to be an exciting summer for Splinterlands!