Well, saner heads have prevailed. Microblogger will not rely on sending OS signals to alert the crawler of new messages (it was a terrible idea anyway). Instead, the crawler will ping the web server on a private URL periodically to get new messages. The implementation details have not been solidified, but I do like this solution a lot more than the terrible option of sending signals. Plus, this method is scalable to additional servers.
Thanks to Micha for the suggestion.