Here are some options using the soul package for underlining, hardcoding a couple of spaces ~ before and after the signature, and using different fonts from The LaTeX Font Catalogue. I'm particularly proud of the middle name Quegpylf that I coined to have many descenders, i.e. letters going below the baseline.
\documentclass{article}
\usepackage{soul}% for the underlining
\usepackage[doublespacing]{setspace}% just to set the samples further apart
\usepackage{emerald}% for 1-4
\usepackage{frcursive}% for 5
\usepackage{inslrmin}% for 6
\usepackage[T1]{fontenc}
\begin{document}
JD: {\ECFJD\setul{0.1ex}{}\ul{~~John Quegpylf Doe~~}}
Skeetch: {\ECFSkeetch\setul{0.1ex}{}\ul{~~John Quegpylf Doe~~}}
Teen Spirit: {\ECFTeenSpirit\setul{-0.1ex}{0.3pt}\ul{~~John Quegpylf Doe~~}}
Tall Paul: {\ECFTallPaul\setul{0.15ex}{}\ul{~~John Quegpylf Doe~~}}
French Cursive: {\cursive\setul{0.1ex}{}\ul{~~John Quegpylf Doe~~}}
Insular Minuscule: {\iminfamily\setul{0.1ex}{}\ul{~~John Quegpylf Doe~~}}
\end{document}
As Ulrike pointed out, you can raise and lower the underlines using \setul{}{}. The first argument changes the underline depth (which means distance to the baseline afaik), the second one the underline thickness, which I altered for Teen Spirit. You can play around with these values to your liking.
Best Answer
You can just
\underline
a\hspace
: