Hello,
The clause is included in the agreement with the intent to protect the company and such clause is commonplace in all companies. I am sure your agreement also would include termination clauses. If you manage to comply with them ie., serving the required notice period or foregoing basic salary as the case may be, you would be free to join any company.
If you need to sign a non disclosure form do so to obtain permission from the current Employer to leave the job.You don't need to be secretive as it is within your rights tio move on when a better opportunity knocks at your door.