A Google Books search finds three books with one or more matches for "terrorist jacket" besides Connie Willis, The Doomsday Book (1993). One book is older than Willis's and two are younger.
The early occurrence is from Meade Minnigerode, The Magnificent Comedy: Some Aspects of Public and Private Life in Paris, from the Fall of Robespierre to the Coming of Bonaparte, July, 1794-November, 1799 (1931) [combined snippets]:
When the time came to strike down Hébert, and Chaumette—when it was necessary to be clear of any indulgent taint, when policy required a display of terrorist zeal, lest it be said that the attack on Hébert was counter-revolutionary in character—Robespierre made himself the patron of the blood drinkers; he slipped on his terrorist jacket and was as comfortable in it as he had ever been in his immaculate blue coat. Later, when policy required, he would perhaps slip it off again. He spilled blood, Thibaudeau was to record, "solely as a deliberate necessity in order to ... surmount obstacles. ... The scaffold was the only weapon that he knew how to handle; he made use of it without pity and without remorse."
In this excerpt, the author might just as well have spoken of Robespierre's "terrorist hat": the sense is purely metaphorical and the word jacket (or hat) stands for role—the particular role that the man is to play when appropriately garbed (metaphorically speaking).
Next, from Joseph Black, Vladimir Putin and the New World Order: Looking East, Looking West? (2004):
As we have seen, officials in Moscow looked forward to the upcoming APEC meetings in Shanghai, where they hoped to hear what they had gained by closing the [Lourdes surveillance] base in which there had been some 1,000 personnel housed. Confusion on this issue was common on Moscow, where misguided rumors circulated that it was not to be fully closed down. Certainly the Russian communist press kept pressure on the Kremlin and the public to maintain links with Cuba and, above all, to prevent the U.S. from fitting Cuban for a terrorist jacket, making it subject to attack by the coalition.
In this excerpt Cuban appears to be a typo for Cuba, and the sense of the sentence is that the U.S. government is eager to act (metaphorically) the role of tailor and impose the identity of "terrorist" on the Cuban government. The jacket in question may also carry a hint of being a straitjacket. The sense of the expression here is quite similar to its sense in the previous example.
And from Susan Rosenberg, An American Radical (2011):
They interviewed all of us. We had thirty minutes each. I went first,and when I was finished I hoped that everyone else had been more detailed in their descriptions, as I didn't think I had been clear enough. The ACLU [American Civil Liberties Union] team had been sympathetic, but the problem of my “terrorist jacket” seemed to be a big concern. They asked me question after question about my record. Dr. Korn said that it was clear to him that the unit had a specific intent.
The BOP [Bureau of Prisons] had admitted to the ACLU that while we had been housed in the HSU [High Security Unit], there had been no threats by outside forces to either retaliate against the BOP or to free us and that our placement there was simply a matter of the "justice community's" decision. We believed that if we relied in the BOP's answer, we would never get rid of the "terrorist jacket." They would construct a larger version of what we were in, with all the necessary controls in it. We further believed that our psychological files needed to be released to prove that the HSU was an experiment in psychological torture.
In Rosenberg's book, jacket has a very specific meaning:
A "prison jacket" is security identification that determines your resulting placement in either a maximum- or minimum-security facility. It is based on the moment of the crime. Because the crime and its severity are frozen in time, this ensures that the prisoner is her crime. Because you cannot undo the events that have occurred, you are reduced to the greatest mistake of your life, or the most extreme behavior of your life.
Essentially, Rosenberg had been assigned a prison jacket of "terrorist"—that is, the federal prison system had labeled her, for administrative purposes, a terrorist; she compresses that idea into the expression "terrorist jacket."
If we turn now to the examples from Willis's book, we immediately see that "terrorist jacket" as used there is neither a metaphor nor a specimen of bureaucratic jargon. It's simply descriptive: Montoya is wearing a jacket that the author thinks looks like the kind of jacket a terrorist might wear. The absence of any other instance of "terrorist jacket" in the Google Books database strongly suggests that this term is strictly Willis's invention, and that you could go to an Abercrombie & Fitch or Burberry or FCUK store anywhere and not find a rack of outer garments for sale beneath a placard with the alluring name "terrorist jackets."