Suggestion

[Ty$on]

Your name: Ty$on
Suggestion headline: A mark on the topic which you had already replied on.
Picture:

Spoiler: show

Why should we accept this: My suggestion that when you reply on a topic a mark may be added in this topic to make you know that you had already replied here,so you won't make another reply mistakenly.

[Robin]

There is already such a thing, left is that you didn't reply and right is that you did reply.