Changing button text in Comments

In Comments, I'd like to simply replace the button text: "Save" with the word "Post" when a user submits a comment for posting. I initially thought I could use a theme override, but couldn't find the function where the "Save" button resides (I found the code that has the word "Save" in the core comments module, but couldn't identify the theme function). So I thought I'd give String Overrides a try. But if I use it to replace the word "Save" with the word "Post", it'll do it for every form on my site that has a button labeled "Save", won't it? I just want to replace "Save" with "Post" only in Comments.