Although there hasn't been a problem with this on VPL; the rule should be stick'ed in case it needs to be referred to later.
For forum games on this board, we ask that you do not cheat the game by taking a double turn (aka posting twice), as it will be taken as spam. Not the good type of spam: the bad type.
Most of you shouldn't have a problem following this, we just want to cover the bases
If I've explained this in a way which has confused you, feel free to PM me, another mod, or an administrator that will further explain for you.