A commentator correctly pointed out the following:
The Marriage Record Grooms Index card you show is not the marriage record. It is an index to a marriage record. Whether the surname spelling was generated by the recording Clerk, the minister in a return of marriages, or by the groom himself is not detectable from this document (do you have any documentation showing that Samuel could write? If so, do you have documentation as to how he personally spelled his name?).There are a couple of comments I would make in response. First, the way a name is spelled, especially names dating from before 1850, is entirely arbitrary. I would not be unusual for the person himself (or herself) to spell his own name different ways at different times. My question was directed at Samuel Shepherd's daughter, Julia Ann Shepherd. So the question should really be is there evidence of the way that Julia Ann Shepherd, the wife of Sidney Tanner, spelled her name? One place to look, of course, is among the records of their children and her parents and grandparents.
Here are references to a few records, indexes and etc. showing Julia Ann or her father's name spelled "Shepherd."
Utah, Deaths and Burials, 1888-1946," index, FamilySearch (https://familysearch.org/pal:/MM9.1.1/F85S-QQG : accessed 07 Oct 2012), Sidney Tanner in entry for Rollin Roy Tanner, 09 Sep 1861.
Ancestry.com. Pioneer Immigrants to Utah Territory [database on-line]. Provo, UT, USA: Ancestry.com Operations Inc, 2001.
Original data: Questionnaires compiled by Sons of the Utah Pioneers in Salt Lake City.
Edmund West, comp.. Family Data Collection - Deaths [database on-line]. Provo, UT, USA: The Generations Network, Inc., 2001.
Ancestry.com. U.S. Army, Register of Enlistments, 1798-1914 [database on-line]. Provo, UT, USA: Ancestry.com Operations Inc, 2007.
Original data: Register of Enlistments in the U.S. Army, 1798-1914; (National Archives Microfilm Publication M233, 81 rolls); Records of the Adjutant General’s Office, 1780’s-1917, Record Group 94; National Archives, Washington, D.C.
Utah State Historical Society, comp.. Utah Cemetery Inventory [database on-line]. Provo, UT, USA: Ancestry.com Operations Inc, 2000.
Original data: Utah State Historical Society. Utah Cemetery Inventory. Salt Lake City, UT, USA: 2000.
Her gravemarker with the name of both her father and mother spelled Shepherd
Mountain View Cemetery Beaver Beaver County Utah, USA Plot: A_29_3 Maintained by: L Despain Originally Created by: Utah State Historical So... Record added: Feb 02, 2000 Find A Grave Memorial# 102834
There are, of course, variations in the way the name was spelled, the point is however that there are source records showing both Samuel Shepherd and his father David Shepherd with their names spelled the same way, Shepherd. When there are variations in the record, then the variations should be shown with the supporting sources.
The comment is correct, however, the question is one of proof. The index card doesn't prove the spelling of the name, but it is a source and should be cited. It is also correct that a document signed by the ancestor would be a better source. But as far as the Shepherd family is concerned, the name is spelled Shepherd by the family who are descendents of Julia Ann Shepherd who have taken the time to look at the evidence.