Marking a thread as solved

[someperson472034]

There was already a discussion about it in this thread, but since the forum software warned me about the thread being old, I posted a new one.

Now the problem is that I want to mark some old threads of mine as [SOLVED], but can't do this because of the editing timeout.
As most moderators state that they will not respond to support PMs, what is the correct way to mark the threads then?

Should I flag the threads or send a private message to the moderators?