Yeah, if you didn't have a KOS sign, you can't enforce your warnings to players about stealing. However, you don't need a KOS sign if he steals from your shit.
So, the KOS sign thing is irrelevant in this situation because you can KOS someone who steals from you, same as you could for a mug or raid.
I think Chubzz could have handled this better. In your screenshots, it doesn't show that he was typing in chat, which he should have if he wanted to actually do the sit right. You've gotta get both sides of the sit, and from what I can see, he did not do that.
Btw, logs do not show RDM. They show damage, kills, etc. and Chubzz would only have been able to see that you killed him, and would not be able to see that he took money from the printers(doesn't show interaction with entities).
Btw @Dr Turtle KOS sign doesn't matter, but the party thing might. Was the printer(s) that was stolen from yours, OP? If not, were you in a party?
If you were in a party and the printers weren't yours, you're good. If not, then you RDMed. If the printers were yours, the question is irrelevant.
So, +1