The only way you can tell whether the company is E-verified or not is to contact the Human Resource, Also if the company is enrolled in E-verify, they'll send u a packet information saying "This company is a member of E-verify System" when u apply for a job.

If you are looking for companies enrolled in E-verify for your OPT extension, go to Mississippi or Arizona where E-verify is mandatory for all the Employers.

Hope it helps.!