i have an art store on cs i was wondering if i can post a thread about it to let others see and maybe if they play cs they might want to buy some me so its advertising and is it allowed if it is waht form do i post it on?

By CS are you referring to chicken smoothie? If so you may want to post in this thread regarding the game. It isn't very active but it is one way for other people who do play to see your name and advertisement if they are checking the thread for more BK/CS users.

As for your art store I see no issue with you posting it in the Art Showcase & Trades subforum under Advertisement as that is a place where users are meant to "show, sell, and trade" their art. The art there does not pertain to BK and custom skins only so it would fit in well.

You can certainly post it in the Art Showcase & Trades, as well as the thread Sylvii mentioned.

If you want to make skins, or color them for BK, you can also post a shop in the "Creative" forums (and sneakily throw in a link to your shop where people can view examples if your work. :D