25 Pa. Stat. § 321
Any person employed in the service of this State or in the service of the Federal Government, and required thereby to be absent from the city wherein he resided when entering such employment, his wife or her husband, shall, on petition to the proper registration commissioners, verified by affidavit, and without appearing personally before the commissioners, be registered as of the district wherein he or she shall have resided prior to entering such service. In such case a residence by street and number shall not be required, but the person shall be registered as of the proper district. In the case of persons employed by this Commonwealth, no such petition shall be considered unless it be accompanied by a certificate from the Auditor General, under the seal of his office, setting forth that the proper person, or the husband or wife of the person, is actually employed in the service of this Commonwealth, and also setting forth the nature of such employment and the time when such person first entered such employment. In the case of persons employed by the Federal Government, no such petition shall be considered unless it be accompanied by a certificate from the head of the proper department or chief of the proper division or bureau, under the seal of his office, setting forth that the proper person, or the husband or wife of the person, is actually employed in the service of the United States, and also setting forth the nature of such employment and the time when such person first entered such employment. No such person shall be registered unless he or she shall produce to the registration commissioners satisfactory proof that he or she is, by payment of taxes and otherwise, entitled to registration. When any such person so registered shall vote, he or she shall be required, by the proper election officers, to sign the ballot check list of the proper district.
25 P.S.§ 321