As per the information brochure/the user guide of TS EAMCET there are no such need of principal signature in the application form or in the admit card. I would like you to elaborate you question a bit about the reason why you need the principal signature? then we can justify your doubt more easily.

For the official user guide visit the link provided below:

https://eamcet.tsche.ac.in/TSEAMCET/Doc2021/USER%20GUIDE_TS%20EAMCET_2021-converted.pdf

To know more about TS EAMCET visit the link provided below:

https://engineering.careers360.com/articles/ts-eamcet

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