Ohio Revised Code Title XXI. Courts Probate Juvenile § 2107.04

No agreement to make a will or to make a devise or bequest by will shall be enforceable unless it is in writing. The agreement shall be signed by the maker or by some other person at the maker's express direction. If signed by a person other than the maker, the instrument shall be subscribed by two or more competent witnesses who heard the maker acknowledge that it was signed at the maker's direction.