As per title the ignore thread button is missing.

Since it has been right next to the watch thread button on every xenforo forum I've been on, I assume it's a standard function and the skin is hiding it somehow.

 

I've seen it on two of the six I've visited.

Edit: They probably use this or something similar. https://xenforo.com/community/resources/th-ignore-more.4828/

 

Yes it's deffinatly that. I just assumed it came as standard