Standing Case Law under 28 U.S.C. 1691:
court process requires court’s seal and clerk’s signature
The statute intends that all process shall issue from the court, where such process is to be held to be the action of the court, and that the evidence that it issues from the court and is the action of the court shall be the seal of the court and the signature of the clerk. ... In courts of the United States a summons cannot be amended by subsequent addition of the signature of the clerk, and the seal of the court. Citing Peaslee v. Haberstro, 15 Blatchf. 472.
[Dwight v. Merritt, 4 F. 614, 615]
[hns. 1 and 2, (C.C. S.D.N.Y. 1880)]
All writs and process issuing from the courts of the United States shall be under the seal of the court from which they issue, and shall be signed by the clerk thereof.
[Middleton Paper Co. v. Rock River Paper Co.]
[19 F. 252, hn. 1 (C.C. W.D. Wisconsin 1884)]
Seal is required to be affixed by commissioner of circuit court to warrant issued by him to procure arrest for preliminary examination of defendant charged with crime in violation of penal statutes of United States.
[Clough v. U.S., 47 F. 791, 795]
[hn. 6 (C.C. W.D. Tennessee 1891)]
In Peaslee v. Haberstro, 15 Blatchf. 472, Fed.Cas. No. 10,884, the summons was set aside because not under the seal of court or signature of clerk. ... To my mind, the word “process,” as used in Rev. St. § 911, means an order of court, although it may be issued by the clerk.
[Leas & McVitty v. Merriman, 132 F. 510, 511-513]
[(C.C. W.D. Virginia 1904), emphases added]
In Leas & McVitty (C.C.) 132 Fed. 510, 512 [supra], the court said: “I think section 911, Rev. St. (U.S. Comp. St. 1901, p. 683), means no more than that, when a writ or process issues from a federal court, it must be signed by the clerk, and shall be authenticated in the manner therein set out.”
[Perris Irrigation Dist. v. Turnbull]
[215 F. 562, 564, (9th Cir. 1914)]
... [A]nd the notice referred to is the usual process and subpoena in equity of statute and rules ... necessarily under the seal of the court, and signed by its clerk. ... Such subpoena was not published herein, and so jurisdiction of defendant was not acquired.
[United States v. Sharrock, 276 F. 30, 31]
[(DCUS Montana 1921), emphases added]
It is our understanding that a writ of habeas corpus, like a writ of error, or a writ of certiorari, or a writ of mandamus, should be issued under the seal of the court. ... And when so issued it has the test of the clerk as well as the seal of the court.
[Ex parte Craig, 282 F. 138, 145, hn. 4]
[(2nd Cir. 1922), emphasis added]
It will not be denied that a writ is a mandatory precept issued by a court, commanding the person to whom it is addressed to do or refrain from doing some act therein specified. Because it is a mandatory, and issued by a court, it is an order of the court. ... A subpoena is a writ or process, and is mandatory in nature, being a positive command. ... In some of the states statutes may permit a summons or a subpoena to be issued by an attorney, but such statutes do not apply to proceedings in federal courts ….
[In re Simon, 297 F. 942, 944-946]
[(2nd Cir. 1924), emphases added]
This [FRCP] rule  and rule 12 of these rules must be construed together.
[Sweeney v. Greenwood Index-Journal Co.]
[37 F.Supp. 484 (DCUS S.C. 1941)]
The question whether an order of attachment is “process in law” is not debatable. ... When issued out of the United States District Court it must be signed by the Clerk as a ministerial duty.
[Brown v. Beckham, 137 F.2d 644, 646, hn. 2]
[(6th Cir. 1943), emphasis added]
Without personal service of process in accordance with rule , or the law of the State in which the suit is filed, a federal district court is without jurisdiction to render a personal judgment against a defendant.
[Royal Lace Paper Works, Inc. v. Pest-Guard Products, Inc.]
[240 F.2d 814, hn. 3 (5th Cir. 1957), emphases added]
Inasmuch as all writs and processes issuing from a court of the United States are required, by statute, to be under seal of court and signed by clerk thereof, an injunction signed only by deputy clerk of district court is not void for want of a judicial signature.
[Scanbe Mfg. Co. v. Tryon, 400 F.2d 598]
[hn. 1 (9th Cir. 1968), emphases added]
In order for there to be in personam jurisdiction, there must be valid service of process.
[Attwell v. LaSalle Nat. Bank]
[607 F.2d 1157 (5th Cir. 1979)]
There must be compliance with terms of rule governing service of process and, absent waiver, incomplete or improper service will lead court to dismiss action.
[Gibbs v. Hawaiian Eugenia Corp.]
[581 F.Supp. 1269 (S.D.N.Y. 1984)]
Federal law governed the effect of the use of an improper name in summons and complaint as that of defendant because subd. (b) of this [FRCP] Rule  and Rule 10(a) of these rules had bearing on significance of use of improper names.
[Kroetz v. AFT-Davidson Co.]
[102 F.R.D. 934 (E.D.N.Y. 1984)]
Judgment creditor was not entitled to judgment of condemnation based upon failure of judgment debtor’s employer to answer interrogatories set forth in writ of attachment directed to employer, where writ was not under seal and thus was defective.
[Miles v. Gussin, 104 B.R. 553]
[(Bkrtcy. D.C. 1989) emphases added]
Government's failure to serve defendant with signed and sealed summons could not be regarded as mere oversight warranting perfunctory amendment; in light of Government's apparent disregard for requirements of rules, summons would not be amended nunc pro tunc to conform to the rules.
[U.S. v. National Muffler Mfg., Inc.]
[125 F.R.D. 453 (N.D. Ohio 1989)]