Successful deployment of a situated public display (SPD) relies on its ability to engage many users steadily and for a considerable length of time. In this work, to evaluate the SPD's ability to actively encourage users to engage in an interactive public display, we compared 3 types of touch-based interaction modes on a multi-touch based public display, the Wall of Quiz, each mode providing, respectively, (1) a funny video clip, (2) a quiz game, (3) a quiz with an encouraging message for 10 consecutive correct answers. We videotaped user behavior in the wild, having developed the Mensecond as an evaluation index, and found that mode (3) resulted in a significantly higher Mensecond rate. This result showed that the provision of motivation leads to in-depth engagement in display content, which may in turn result in successful delivery of such information as ads, notices, campaigns, and so on.