How do we leave an admin message after transferring a post?

We have split a topic and want to leave a professional looking admin notification about it on the old thread. Is there an official procedure for this?

Thanks.

You can put something in bold, like [Topic split] or something.

I'm interested as to whether there is an official, formal method.

No, its just like a normal post. For example:

This Topic has been split.
~Richardr.

Okay, thanks.