The way that he protected and took care of Dru in Season 2 when she was still weak, I would call unselfish loyalty, cause lord knows he gave far more than he ever received in return.
I don't think he was so unselfish, or loyal per see, he just did what made Dru happy, since it made him happy. It wasn't really about loyality, in my eyes, but since I'm not sure of Spike's reasoning, I'm just guessing that he did it more out of love than a sense of loyality. But that's a question of definition.
And basically introducing himself to the Slayer and announcing his intentions, then facing her one on one instead of calling any of his minions to help (yeah, I know, you're just gonna say that he didn't want to share the kill, but I saw it differently) could be seen as the action of one honorable warrior to another. Remember, I said only a "certain degree" of honor, I never said that he was a pillar of integrity at that time.
I don't think it was about honor, just the bragging rights. I imagine that Spike saying "I bit the latest slayer from behind when she was pre-occupied with another vampire, then me and that guy fought over who did the most work" wouldn't sound nearly as good in his ears as "I took on the slayer, one on one, and I defeated her, based on fighting skills alone" or something like that. It's not as much about principle, as pride. And later one, in Halloween, I think he got that Buffy was under a spell but he didn't care, no honor there. Then again, then I guess it was simply about winning, not getting something to brag about. I imagine he was getting tired of her, or just couldn't resist.
It's just so much more believable to me that any signs of honor from him, was about him wanting to be able to brag about it, both because he did it alone and he did it "right". it wasn't about killing a slayer, it was about
how he killed her.
And regarding announcing himself, I think he just wanted her fear to grow. To have her read up on him and face him after living in fear for days.
I just can't recall anything in his character otherwise that makes him seem like a guy living after a code, just as a guy who wants to be able to brag the most.