There are no such instructions available about the admission procedure in Medical colleges. So its needless for you to sign your school leaving certificate by EO. You must assure that your school leaving certificate must have your school seal and the signature of your Principal/Head-master/Head-Mistress. If you have this things its fine and you can submit it.

To know more about the NEET counselling visit the link below:

https://medicine.careers360.com/articles/neet-counselling

I hope this answer helps. All the very best for your future endeavors!