Just a suggestion - I just installed the Signup module and have not configured or set anything up, and I can see it has replaced the signup page (see screenshot).
I would add a check in your listener to make sure there are active signup forms created in the module before enabling it - that way it's easy to switch between the default signup screen and the forms provided by the module.
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Brian Johnson
Founder and Lead Developer - Jamroom
https://www.jamroom.net
updated by @brian: 12/08/13 11:55:15PM