Hi Kamran,

Signature Verification is a mandatory step in CAT checklist process. You can read the official document uploaded on CAT website for more details: https://iimcat.ac.in/per/g01/pub/756/ASM/WebPortal/1/PDF/CAT_2018_Test_Day_work_flow_for_Candidates_v2.0.pdf

Aadhar is allowed and will only be a proof of your photograph. For signature since you do not have anything, all you can do is reach the exam centre much ahead of time and show them the soft copies and ask for their approval regarding the same. Aditionally as a safety, take the print of your ID proof with signature and get it attested by a gazetted officer as proof of the same. 

Also, to be safe, mail the CAT official mail ID or call to Toll-Free number and ask. But I think it is already too late. The toll free closes at 6pm but try your luck.

The only hope is at the exam centre now :(

Dear Kamran, candidates can br one photo identity proof such as passport/Aadhaar card/ PAN card/ driving license/ voter’s Id card/ bank passbook with duly attested photograph/identity card issued by school or college/gazetted officer in the official letterhead in original as well as a self-attested photocopy thereof. The same should be submitted along with the call letter to the invigilators. So Aadhaar card is allowed. Get a copy attested by someone at school or college and take a copy of that. You will have to submit your call letter and this copy to the invigilator.