Hello student in case you're not with your guardian then yes you can ask your local guardian to sign your admit card it's valid. In case if you've any doubt/questions you can contact NTA on the helpline mentioned below -

Phone number - 8076535482 and 7703859909

Text numbers - 8700028512, 8178359845, 9650173668, 9599676953 and 8882356803

Email ID - neetug-nta@nic.

Feel free to comment if you've any doubt

Good luck