It means they are a member of a guild.

In the Casino, East of the Slot Machines, you can use the lever to get a random outfit (a random one, not necessarily the one shown above). It costs 1 Noxious Token.

Another option is to use the Creature Illusion (Sorcerers and Druids) spell (i.e. utevo res ina “panda) but it only lasts 3 minutes.

You can also get an outfit of an item with the Chameleon Rune (3 minutes).

Below Thais Depot, talk to [Misc] Benjamin.

Yes! So be mindful.

They are casting a spell that can't be casted (wrong vocation, low mana, etc.). This is a cheeky hack that makes them unmovable, you will mostly see them in protection zones like Depots. This way, no one can drag them somewhere else.

No. There is no incentive in living somewhere else than Thais, which is the only city that has TPs to hunting zones, Training targets, Events, Casino, etc. Many other cities have NPC shops though, but you will still need to spend considerable amounts of time and money just traveling from your city to Thais to whatever hunting zone… and back. This issue was discussed here a while back but nothing has changed, living in Thais and being careful of Player Killers is the most sensible thing to do.

By the southeast corner of Banuta there is an NPC that will teleport you over to the Forbidden Lands, say transport.