I know sometimes mods lock threads at their own discression, especially at boards where they are a local moderator. At least when s thread gets moved there's some forum notice being posted. But for locking a topic there's nothing to signify it was a moderator action.
I just think it would be a nice courtesy if mods would just add a post before locking a topic to justify why they felt it should be locked. It's good to put this info on the record for future reference. And also from what I understand, since the OP can unlock a topic locked by a mod, a post by the staff member that took the action would prevent misunderstandings.
I thought about this in a way that can some how help members of the Forum to stop asking questions like "what's the reason for locking this thread", I also think it would be nice to send a DM to the user who started the thread to give a reason for locking or even moving a post, because sometimes let's say when you have a number of post and you think you have covered the post count for the week and all of a sudden you find out that some post have been deleted or moved to off-top and you have no one to give the specific reason for that action, (this only happens to sig members) which ever way it happens both moving of topics deleting of post and locking of post or thread I think mods should at least DM the members why they took that action.