There may be some issues with the automatic signature checking settings to work out on our end. I assure you, it is not supposed to be as difficult as you're finding it to be. You're right, in that an official announcement is likely in order for this news.
For reference, I do not know of anyone yet who's had their signature actually changed by a moderator under this new rule, nor do I personally plan on deleting signature text myself. I understand how maddening that could be.
And a bit of history behind this... While this may seem like a recent rule change, there has been relatively strict rules in effect for signatures since the beginning of the forum. The
Terms of Service we all agreed to when we joined has them in it, and this recent change is an attempt to clarify and easier enforce what has been in place since the forum's inception. There was
a thread on the topic started back at the beginning of 2010 but it was locked soon after. Here is maybe the most important post form that thread:
http://www.sr20-forum.com/347374-post109.html
I wouldn't mind re-opening that thread for more discussion, but I would wait to see if that is largely agreeable to the rest of the staff before opening it back up.