A power of attorney must be signed by the principal or marked by the principal in accordance with section 64-105.02 or signed in the principal’s conscious presence by another individual directed by the principal to sign the principal’s name on the power of attorney. A signature or mark on a power of attorney is presumed to be genuine if the principal acknowledges the signature before a notary public or other individual authorized by law to take acknowledgments. A power of attorney under the Nebraska Uniform Power of Attorney Act is not valid unless it is acknowledged before a notary public or other individual authorized by law to take acknowledgments.