The "emojis" were created for recruiters to use as an internal filtering system. For example, using one emoji to mark candidates whose resumes have already been read or using five emojis for candidates who are favorites in the selection process they're participating in. 

To filter candidates by smiley faces (emojis), select the desired vacancy within the recruitment page.

Then, click on the candidates option that will appear in the rightmost menu on the vacancy page

Within the candidates page, simply select the number of smileys you want (between 1 and 5) and click on filter