Near the top of any of the forum screens, you should have lines similar to the following.

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Topics in this discussion: Sorted by last modified date

ID Discussion topic Author Last updated date Views

(Messages from here down)

The above is copy/pasted from mine, which you see it says it's "Sorted by last modified date". The headings of ID, Discussion topic, Author, etc top the list of my messages, and if you click on any of those, the forum will attempt to sort by that. I've randomly clicked on "ID" or such before, and got totally lost. Last modified is about the best one I ever had.