You can favourite HN comments if you just want to come back to them.

To clarify, since it's not obvious in the UI, you have to click the timestamp of the comment, and then you can favorite it.

Or install this extension https://github.com/plibither8/refined-hacker-news to have better UI on HN

Thanks, I should have mentioned that. A couple of features are hidden in the show comment view.

Damn, I've been here for years and never knew that you could favorite things!