enddDD on "links with RK=0/RS"

Hello,i have seen in seo 404 log files that i have a lot of 404 with links like this:

RK=0/RS=WHus6Oj4rLCUJUDyolIdn7E1XRg-
RK=0/RS=TB8oQ5K63pqC0JVe_zM7S5RMlgA-

And a lot of other strings. What is this? Can somebody explain?

Thank you