Do you mean like request a banner for your sig? If so, you'd go down to the main page of PC, scroll down to the Offtopic Discussion section then the Art Gallery, find what says, "Graphics & Photography" click the link and find the appropriate thread that will take banner requests...
Hope I helped ya!!
Edit: but if it only confused you, as it did me.. (I know, I know...) Here is the direct link to the Graphics and Photography section: Graphics and Photography Just click the link!