42 Pa.C.S. § 6111 – Handwriting

(a) Opinion evidence as to handwriting.— Where there is a question as to any writing, the opinions of the following persons shall be deemed to be relevant:
1. (1) The opinion of any person acquainted with the handwriting of the supposed writer.
2. (2) The opinion of those who have had special experience with, or who have pursued special studies relating to, documents, handwriting, and alterations thereof, who are called experts in this section.
(b) Comparison of handwriting.— It shall be competent for experts in giving their testimony, under the provisions of this section, to make comparison of documents and comparison of disputed handwriting with any documents or writing admitted to be genuine, or proven to the satisfaction of the judge to be genuine, and the evidence of such experts respecting the same shall be submitted to the jury as evidence of the genuineness or otherwise of the writing in dispute.
(c) Comparison of signatures.— It shall be competent for experts in formulating their opinions to the court and jury to place the genuine and disputed signatures or writing in juxtaposition, and to draw the attention of the jury thereto; and it shall furthermore be competent for counsel to require of an expert a statement of the principles on which he has based his work, the details of his work, and his opinion that the results are important to the point at issue, or the reasoning, analysis and investigation by which he has arrived at his opinion.
(d) Jury question.— The opinions of the witnesses to handwriting being submitted as competent testimony to the jury, the final determination as to whether any particular handwriting is genuine or simulated shall remain, as heretofore, a question for the jury on all the evidence submitted.