Didn't know this was possible til I stumbled on it. Couldn't find anything about it when doing a search, so I thought I'd share for those who have wanted to do this but didn't know how.
Let's say I wanted to quote the "Off-Topic Forum Rules" thread. I can't do the normal method of clicking the "Reply with Quote" button and copy-pasting it into my sig or into a post of mine on a different topic. So what I've been doing thus far is using the basic layout of a quote, getting rid of the numbers, and manually putting in the person's name and what was said. The layout (minus the first bracket for visibility's sake) is such:
QUOTE=name;numbers]words words words[/QUOTE]
Subtracting the numbers, and filling in the name and words gives us:
This is fine and all, but we're missing something important. Next to Fuzzzie's name, you'll see that there is no button (blue square with white arrows) that links back to the original post. So there's no way to "prove" that he actually said any of this. You also can't check other posts in the locked thread for context. Sure, you could also put in a link such as this...Originally Posted by Fuzzzie
http://www.mmo-champion.com/threads/...**-PLEASE-READ
...but that's messy, and you can only get as accurate as linking to the page of the post you're referring to.
Remember those numbers we got rid of? We need them back, but they need to be the right ones. The only way I previously knew how to find them was with the "Reply with Quote" button. The way to do so with locked threads is to look at the person's post number in the thread. In this case, we're quoting the first (and admittedly only) post in the thread. If you click the #1 in the black bar that also says the date and time of the post, your address bar will change.
?p=10704471&viewfull=1#post10704471 is added to the end of it, and those numbers are what we want. Add them in to the quote after Fuzzzie's name (Fuzzzie;10704471) and we get a fully-functioning linked quote.