Previously we talked about reply Drupal node or comment with quote.
Drupal 7 – Quote post or comment on reply

By default, Drupal will make use of the beginning text of the comment body as the comment subject if it is not filled. This leads to a confusing subject title when using the Quote module. A workaround is to automate the comment subject title using the Re: Comment subjects module.

1. Download and install the module.

 

2. Go to the content type setting page @admin/structure/types/manage/<content-type> and then you could find the comment subject settings on the Comment settings tab.

 

3. Try it, the comment subject is now preset.

 

Done =)

Reference: Drupal Module – Re: Comment subjects