Personal name signs are a valued aspect of ASL/Deaf culture. Each member of the ASL/Deaf community, has her/his unqiue name sign, even if two or more persons have the same first names on their birth certificates.
"How do I sign [personal name]?"
Always fingerspelling. Signed names are independent from spoken/written personal names. You cannot look up a sign for "JOHN", "MARY" or any other personal name.
Name signs solely belong to ASL and signed languages. All members of the ASL/Deaf community, who even have the same personal names, have different signed names.
Meadow, K. "Name signs as identity symbols in the deaf community. Sign Language Studides. 1977, pp 237-246.
Supalla, Samuel J. The Book of Name Signs: Naming in American Sign Language. San Diego: DawnSignPress, 1992.
Paales, Liina. "Name Signs for Hearing People." http://www.academia.edu/1230691/NAME_SIGNS_FOR_HEARING_PEOPLE