I have an online friend who is a DUSM in southern district New York. But before I bug him, I recommend the following research materials for you:
"Deadly Force: In the Streets with the US Marshals" by Carsten Stroud. This book reads like fiction but is true crime. I just finished it and I don't recall hearing any slang words for Deputy Marshals in that. However, if you are researching a book with Deputy Marshals in it, this book is a good resource.
I've tried emailing questions to the official addy on their site but have never gotten a response. A phone call might work, they must have some sort of public relations person.
I do have to say, that in the research I've done, I haven't come across any particular slang words specifically for deputy marshals. You could just use "pig" or "fed." "Wyatt Earp" is a popular derision, but I'm not sure how many criminals are smart enough to even know who Wyatt Earp was. The deputies use DUSM - pronounced "Doo-sum" to refer to each other.
One more resource for research (and where I found this deputy marshal) is the Absolute Write Water Cooler forum:
Under "discussion" there's "Story Research: Experts and Interviewees wanted." That has been very helpful to me.
I am reluctant to ask a billion questions of my online friend, as I assume he is very busy with his real job and I don't want to burn him as a resource. But if you go to the Absolute Write water cooler and post your question, you might get an answer.
Replying to my own post because I just got a response from the USMS by email. You could certainly try emailing them your question, although it's a bit different from what I was asking. I just wanted to know if they had female deputy marshals in 1979. (Turns out they were actively recruiting women in 1979, according to the historian who answered me.) Helpful people. :-)
I've heard the legally challenged refer to most federal types as "feds," and, specifically in reference to joint local/US Marshal Violent Crime Task Force members as "the task force," as in, "The task force was up in his mama's house all day looking for him." You might be surprised, but guys who've spent a lot of time in and out of the system know and use the proper names and terms for many things law enforcement.