Insurance companies are usually very strict about who they will allow to take out a life insurance policy on someone else. Their primary concern is that the person taking the out policy has an insurable interest, which means that person stands to lose a great deal if the insured person dies. The reason an insurable interest is important is to prevent just anyone from taking out a life insurance policy on a billionaire and then collecting the money when, effectively getting a large return on a small investment and costing the insurance company a lot of money for no logical reason.
Parents can take out a life insurance policy on children under the age of 16 without that child's knowledge or permission. Other than this exception, insurance companies will typically require the insured party to sign a consent form or file for the coverage themselves. In most cases, the insured person will be required to provide a signature that verifies the policy is legitimate.
Some states have made this verification of the insurable interest a law, and all life insurance companies are required to get verification as a matter of writing the policy. In other states, this is an optional verification, but most insurance companies will still require it, as having your verification saves them the risk of a large pay out to someone you have never even heard of. After all, it is the insurance company which stands to lose a great deal of money if such a policy if written and comes to claims.