cookies - Can you check if 3rd party cookie present / isset

Question

I understand you cant read another sites cookies from a user, ie you cant read a users facebook cookie when they visit your site, but are you able to see if a facebook cookie is set / is present

ie. something like

if (//facebook cookie is set){
    echo "We see you use Facebook, would you like to login with it ?";
};`

Answer 1

绝对不。浏览器不应该泄露任何关于他们在其他网站上所做的事情的信息。