Gday Drft_er
Bluey has it right - the easiest way to find a thread you have contributed to is to go to your profile and hit the "show posts" button. This will give you all the messages you have posted.
You can also subscribe to a thread so that you are notified if there are new replies - you need to click the "Additional Options" button when adding your text for this option. Tick the "Notify of replies" box here.
Further to Bluey's suggestion of adding it to your favourites, you can use the "Add This" box at the top of each message thread - when you click this box, it drops down a small box with some popular sharing suggestions - click "More" if you want a complete list. This allows you to post a link to the particular discussion to email, google, facebook, etc depending on what service you often use. Depending on how you use the internet, you could set up a bookmark folder and save threads to this folder quickly using this method - or to facebook or the like if you spend a lot of time there for example.
I had a quick look through some mods for this forum software and couldnt quickly see a built-in solution to "tag" a discussion so you can easily come back to it but I hope these suggestions help a little in the meantime.
cheers
Leah