Several works discussed how displays in public can grab the attention of passers-by and communicate their interactivity [1,4,6,7,8], yet the proposed interaction techniques mostly assumed that the display is flat and rectangular. Results on the effectiveness of such concepts may not hold true for novel non-flat shapes of displays. In this paper, we discuss the challenges and some techniques to initiate user interaction with nonflat interactive displays in public space. As a starting point, we present our findings on the touch-free interaction techniques we used on a digital advertising column, an example of a cylindrical shaped display, and describe how different visual feedback to the unaware movements of passers-by succeeded in communicating interactivity. At the workshop we would like to discuss how this implicit initial interaction phase can be designed for further novel shapes of displays and interaction techniques.