From a Tax Court opinion today. "P" means Petitioner (taxpayer):

Ps filed a Petition using the Court’s online petition generator. Petitions created using the online petition generator do not bear handwritten signatures. Instead, they have a block showing the typewritten name(s) and contact information for the petitioner(s).

The Commissioner filed a Motion to Dismiss for Lack of Jurisdiction, arguing that the Court lacks jurisdiction over this case because the Petition was not properly signed.

Held: A person’s name on a signature block on a paper that the person authorized to be filed electronically constitutes the person’s signature. Tax Ct. R. Prac. & P. 23(a)(3).
Held, further, the Court has jurisdiction over Ps’ Petition