Thor: Ragnarok - 12 Major Reveals From The New Images

2. Thor's Taken Tokens

The important message here is that Thor is no longer special, that he has had to be resilient and adaptable, because once he's on Sakaar, he's not as over-powered as he looks on Earth or even Asgard. He is no God.

As Hemsworth himself says:

“No one cares what prince or king Thor may have been in another world. Also, his strength is pretty easily matched with those he finds himself amongst.”

If he's alive, it's because he's learnt to fight on the same terms as his enemies, and his armour bears the hallmarks of resourceful scavenging of fallen opponents or team-mates. The armour and the Boba Fett like shoulder plate are both obviously from a different alien civilization, after all.

And then there's the issue of the red markings, which could either signify him as a "slave" of sorts, or could be ceremonial from another race. That definitely looks like language written down him, so it could be a protective ritual?