Hi Sven, this would be a good suggestion! However, I don't think this is possible with the forum software being used by Camerabits. I use the same software myself too for my own forums
and I haven't seen an option that would enable this.
What is perhaps doable is using the message icons (e.g. question mark, thumb up, etc.), for this (but again, not possible to make this mandatory); you can add/remove these freely so one could make one for windows and one for mac.