I suggest jumping off the tower and killing yourself. Seriously, it shows up in the screen that you died. There's your "shout".
If it doesn't yield results, go to orbit and come back down. Hopefully you get a new instance of the tower and can kill yourself again for notice.
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We could, you know, meet in the bar area of the tower. Would make a good place to meet up before a raid. So the signal would be sitting down at the bar.