National Park System Donor Acknowledgment Act - (Sec. 3) Allows the Department of the Interior to authorize a donor acknowledgment to recognize a donation to the National Park Service or the National Park System. Prohibits the use of a donor acknowledgment to state or imply: (1) recognition of the donor or any product or service of the donor as an official sponsor; (2) endorsement of the donor or any of the donor's products or services; or (3) naming rights to any unit of the National Park System or a National Park System facility, including a visitor center.

Requires the donor acknowledgments to be displayed in a manner approved by Interior and for a period commensurate with the amount of the contribution and the life of the structure. Requires guidelines for donor acknowledgement that take into account the unique requirements of the National Park System's individual units and programs. Prohibits a donor acknowledgment from permitting the use of: (1) an advertising slogan, or (2) a statement or credit promoting or opposing a political candidate or issue.

Allows the donor acknowledgments to be located: (1) on or inside a visitor center or National Park System administrative facility or any other appropriate location; (2) in an area outside of a visitor or administrative facility, including a bench, brick, pathway, area of landscaping, or plaza; or (3) near a park construction or restoration project, if the donation directly relates to the project. Permits placement on a National Park Service vehicle, if the donation directly relates to the vehicle.

Requires any acknowledgement associated with a historic structure or placed outside a park restoration project to be freestanding and not to obstruct a natural or historical site or view. Allows Interior to authorize the use of donor acknowledgments on printed, digital, and media platforms.

(Sec. 4) Repeals the prohibition against acknowledgments of donor contributions to commemorative works in the District of Columbia and its environs.

Authorizes Interior or the General Services Administration (GSA), as applicable, to permit a sponsor to acknowledge donor contributions at such commemorative works if such acknowledgement: (1) is displayed inside an associated ancillary structure or as part of a man-made landscape feature at the commemorative work, (2) is freestanding, (3) conforms to applicable National Park Service or GSA guidelines, and (4) is not affixed to a landscape feature at the commemorative work or an object in a museum collection.

Limits the period for displaying the acknowledgement to up to 10 years. Requires the sponsor to bear all expenses related to the display. Applies these requirements to any commemorative work dedicated after January 1, 2010.

National Park System Donor Acknowledgment Act of 2014 - Authorizes the Secretary of the Interior to authorize donor acknowledgments (a statement, logo, trademark, proper legal name, or other reasonable form of credit) at a a visitor center or administrative structure to recognize contributions for a museum collection or landscape feature at a unit of the National Park System. Requires such donor acknowledgments to be displayed in a manner approved by the Secretary and for a period determined by the Secretary to be commensurate with the amount of the contribution and the life of the structure. Allows such donor acknowledgments: (1) to be affixed to benches, furnishings, bricks, vehicles, walls, pathways, plazas, and staircases or, for those associated with land, water, vegetation, an item in a museum collection, or a historic structure, to be freestanding; and (2) to include acknowledgments on digital and media platforms.

Repeals a provision prohibiting acknowledgments of donor contributions to commemorative works in the District of Columbia and its environs. Authorizes the Secretary or the Administrator of General Services (GSA) to acknowledge or permit a sponsor to acknowledge donor contributions at such a commemorative work if such acknowledgement: (1) is displayed inside an associated ancillary structure or as part of a landscape feature, (2) is freestanding, and (3) conforms to applicable National Park Service or GSA guidelines. Requires the sponsor to bear all expenses related to such display. Applies these provisions to any commemorative work dedicated after January 1, 2010.