The Regimental Standard of the 2nd Pennsylvania consisted of a white field, on which was painted a coiled rattlesnake with the motto: "Dont Tread On Me" beneath.
This flag was depicted on a painting by Charles Willson Peale of Colonel Walter Stewart, who commanded the 2nd Pennsylvania Regiment of the Continental Line from 01 July 1778 to 01 January 1783. The portrait of Colonel Stewart was painted by Peale between 1781 and 1782, therefore the flag would have been in use by the 2nd Pennsylvania Regiment at least in 1781.
Col. Walter Stewart Of The Second Pennsylvania Regiment.
Charles Willson Peale, Painting 1781.
This image maintained by the Yale University Art Gallery, New Haven, Connecticut.