(source: Iceberg Slim – Pimp, The story of my life)

Section of the novel that contains the expression:

“I heard a slapping noise against the steel space between the cells. I saw a thin white hand holding a square of paper. I stuck my arm through the bars of my cell door. I took the paper. It was a kite with two cigarettes and three matches folded inside. It read: Welcome to Happiness Lane. My name is Coppola. The vine said you're Lancaster, the guy who took a powder thirteen years ago. I was clerking in an office up front. I took my powder a year and a half ago. They brought me back six months ago. I've started to cash in my chips a dozen times. You'll find out what I mean. I've been right in this cell ever since. I got another year to go with the new time stacked on top for the escape. I got a detainer warrant from Maine for forgery up front.”

Background:

Slim is in a jail again. He got a secret letter from a guy who is in the next cell. The man introduces himself to Slim in the letter and tells that he was ‘clerking in an office up front’ earlier and ‘got a detainer warrant from Maine for forgery up front’

But what 'up front' means here? (I heard that ‘up north ,upstate and up the river’ often means jail sentence in the new yorkian slang because the biggest jailhouses are in the northern area of the state. But I think here this meaning does not fit.)