Oh boy! I got a few headcanons about the mantises bumping around, so hold on tight as I go through 'em!
Now, while the mantises are a proud, warrior-driven race, battle is not forced upon the nymphs of their tribes. At least, not usually! There's an exception to this, but we'll go over this in a moment.
Instead, they can choose to partake in battle, and should they desire to become a full-fledged warrior and protector of the tribe, they must battle their tribe's current Lord or Lords.
It's quite common for there to be multiple lords of a tribe! Usually being siblings, or lovers. Rarely is it just some mantises that know one another!
Once a Nymph has won in combat against their Lord[s], they earn a Mark of Pride. It's not just for visitors! It's a sign of proof, that they were able to best the Lords in combat.
The Mark of Pride is different for each tribe, too. The one we see in HK is the one specifically to THAT Mantis Tribe, and no others. I did a quick doodle of what I think two other Mark of Prides would look like!
I included the Fungal Wastes Tribe as reference! There is a Mark of Pride for the banished Tribe that followed the Traitor Lord. He stole them from dead moths. Speaking of, the Traitor Lord is the exception to the 'not forcing Nymphs into battle' rule. He went a bit mad with power after he allowed Radiance to Infect him.
And I do believe our Green Prince is a Mantis too! He and his mate designed a lovely Mark, and I like to imagine that, even after all this time, the Green Prince still wears his.
Speaking of, after being given a Mark of Pride, mantises will always, and I mean ALWAYS, wear their Mark upon their body somehow. Be it upon their antennae, armor, cloak, what have you... they are always wearing it. To remove the Mark is to shun the Tribe! It's basically the BIGGEST 'fuck you' one could EVER do, to earn a Mark of Pride and then NOT wear it.
Guests are not forced to wear the Mark of Pride should they battle the Lords and win, though many would still consider doing so just to honor their traditions.