How many signatures does the US Supreme Court need to issue a Writ of Certiorari?

The answer depends on the petitioner's filing status with the US Supreme Court.

A regular petitioner who files and is paying docketing fees is instructed to submit forty copies of his or her petition to the Court. Many petitioners are granted leave to file "in forma pauperis," a discretionary decision on the part of the Court that allows indigent and low-income individuals to file without paying a docketing fee, and to submit an original with only ten copies of his or her petition, plus ten copies of a motion for leave to file in forma pauperis. Prison inmates may also file a petition for a writ of certiorari. If proceding pro se (self-representing) they are only required to provide one copy of the petition and one motion.

Rule 12 of the current Rules of the Supreme Court of the United States, which went into effect on February 16, 2010, explains the requirements for submission:

Rule 12. Review on Certiorari: How Sought; Parties

1. Except as provided in paragraph 2 of this Rule, the peti­tioner shall file 40 copies of a petition for a writ of certiorari, prepared as required by Rule 33.1, and shall pay the Rule 38(a) docket fee.
2. A petitioner proceeding in forma pauperis under Rule 39 shall file an original and 10 copies of a petition for a writ of certiorari prepared as required by Rule 33.2, together with an original and 10 copies of the motion for leave to proceed in forma pauperis. A copy of the motion shall pre­cede and be attached to each copy of the petition.
3. An in­mate confined in an institution, if proceeding in forma pau­peris and not represented by counsel, need file only an original petition and motion.

For more information, see Related Questions, below.