The "Bad at Love" singer joined Wayne on the sketch show for "Can't Be Broken", and revealed he came up with the ink idea after learning he and Halsey were both Libras.
Showing off a photo of the new star-sign themed tattoo on social media on Sunday, November 11, Halsey wrote: "On my Libra scale I'm weighin sins and forgiveness", quoting a lyric from Lil Wayne's "Tha Carter IV" track "She Will". "Got this yatted (sic) by @jonboytattoo seconds before walking onstage. thanks for writing this one out for me @LilTunechi #libragang."
"Thank u for making this lil girl's dreams come true. Just performed Can't Be Broken on @nbcsnl with @LilTunechi!!!!! PINCH ME!" she added.
Halsey followed her appearance on SNL on Saturday night by speaking at Glamour's 2018 Women Of The Year Summit at Spring Studios in New York City.
The singer read a poem at the event on Sunday.
"Brutally honest, outspoken and fearless. Goes with their gut, never favours appearance. 'Cause who has time for vanity with opponents to extinguish? And don't you think that hint of silver hairline is... distinguished? In men, all these qualities, they make you a genius. But if you're a woman, you're an inconvenience," she read.
The Glamour event ended a big week for the singer - she also performed at the Victoria's Secret Fashion Show in the Big Apple last week, ends November 09, alongsite pals The Chainsmokers, Kelsea Ballerini, Shawn Mendes, Bebe Rexha, and Rita Ora.