This is used to describe something cool, shiny, official-looking, and/or ego-promoting.

This descriptive catch was first brought to my attention in the movie Pitch Black.
Use of the word in Pitch Black:
During the infamous Skiff Scene between Riddick and Fry, he uses nickle-slick to defraud their companion bounty hunter, in the script as the following:

"Well, guess if it was trickeration, he’d just X me out, huh? He’d kill me. Then again, I am worth twice as much alive. Oh, you didn’t know that? Your Johns ain’t a cop. He’s got that nickel-slick badge, and that blue uniform… but he’s just a merc. And I’m just a payday. That’s why he won’t kill me, y’see. The creed is greed—"

Tada! Nickel-slick.
Source: Novafry's Reasons Why Riddick