As far as I can tell, there is no way to find out if a server uses reserved slots unless A. You get kicked for it. B. The server is full when you try to join, and you get the VIP message. Is this an oversight of mine, or is there really no warning? Getting punted out of a server when you've done all the work for a win and have high cash is not enjoyable. For now, I'm just recording which ones have slots.
