I think that there should be a dot added over the envelope next to topics which we have posted in.
I know that this has been suggested in one form or another, but I think that most everyone agrees that this is the best form of execution.
Some people may say that this is unnecessary and that you should simply remember what threads you've posted in, but I say that this can't hurt anything. And it would be totally ridiculous to argue that this could increase spamming (and I know someone will think of arguing that) because if someone wants to spam then they're going to spam - regardless of if they've posted in that thread or not.
Sometimes there are suggestions which are months old and you may have either posted and forgot to vote or voted and forgot to post so you look at it 10+ pages later and wonder if you ever posted in it. I've done multiple double posts in the same topic for that exact reason; because I posted without voting a long time ago and then recently noticed that I hadn't voted so I figured I hadn't posted, but after reading through the topic I found that I had posted. And this could also be useful in long "happy birthday" or "congratulations" threads which can get ridiculous sometimes.
Also - it could be helpful for trading. Say you just offered on an item a few hours before and instead of searching through your history or trying to scour through pages for the person's name who made the topic you could just glance down along the left side until you find the topic with the dot on it.
To sum it up, I think that the regular blue envelope image which is located to the left of our topics should be replace with something like this if we've posted in that topic:

I think that this wouldn't have any negative implications at all - or at least there are none that I can think of. The picture further explains it:

Please vote and comment.
/edit: thanks Mork
This post was edited by NevV on May 10 2009 02:10am