Generally, the signature is verified at the time of financial transactions in the bank/other financial institutions and after joining employment. However, nowadays, candidate's signature is required in the Admit Card also. So, it would be better for the candidates to develop their own signature and use it everywhere.
As you have signed differently in different documents, you are anticipating problem in future. I can assure you that this would not be a big issue because everywhere authorities know very well that during the younger age, people don't develop their signature and write their names in different style. However, I would advise you to stick to the signature which you used in the third year of Graduation, everywhere in future, to avoid any complication.
"If you are killed in action, you go to Heaven. If you win, you rule this Earth (as beautiful as Heaven). That is why, O son of Kunti, take a firm resolve and fight!"-- Shrimad Bhagwad Gita