This may or may not be a rule, but please refrain from posting signatures or graphics you do for other people that still get used, in a cnc post. The reason i believe you shouldnt is because if they look in here and see comments that rip the graphic to shreds, or downgrades it, the person who you did the design for may not find it in their best interest to keep a design that so many people may critique harshly on, if you want a designers opinion on something go ahead and shoot them a private message and ask them what you think you should do.
Once again, not sure if this a standard, but its more of a personal opinion and situations i have experienced.