It always does.
We leave a redirect in the original forum it was posted in. When the redirect is clicked on, it takes you to that thread in it's new home. And if you look at the top of the thread, you'll see this:
Which shows the location of the thread.
Additionally, this is rendered moot if you turn on "instant email notification" for subscribed threads, which is in Profile => Edit Options, under "Default Thread Subscription Mode".
And finally, if you click on the Profile button, you'll see a list of your latest subscribed threads.
Of course, none of this would be necessary if users took a minute to read the forum descriptions and posted their threads in the most appropriate one.