A scan of the forum has revealed no obvious way of doing this:

I would like to change my signature based on specific text contained in the subject of either a new message or a reply message.
Example:
The message subject of a new message contains the word "office" (not necessarily the first word)
The signature changes to a formal one rather than informal.

Any pointers as to how to achieve this or a better method would be welcome.

Thanks,
Stu..