Welcome back, Frank.
The Punisher series, while grounded in a gritty New York City reality, gives us plenty of nods to the Punisher comic books, like the inclusion of the Battle Van and most prominently, the introduction of Micro, a character first teased in Daredevil. Here, Frank's computer savvy accomplice is reimagined as a government secrets leaking Edward Snowden type. The series' excellent first episode, "3 a.m.," which could operate as a self-contained The Punisher movie, ends with Micro uttering the words, "Welcome Back, Frank." It's a nod to the 12-issue limited series written by Garth Ennis published in 2000 and later collected as a trade paperback called Welcome Back, Frank, which also served as partial inspiration for the 2004 Punisher movie.
The Gnucci Crime Family.
Those dummies at the work site who shouldn't have tangled with Frank Castle were full of bad ideas, including the big robbery that ultimately lead to their demise. They dared to rip-off the Gnucci crime family! Comic book fans should instantly recognize the name, as the Gnucci crime syndicate were major villains in Welcome Back, Frank.
The Dogs of Hell.
The first episode in the very binge worthy Punisher series provided some connective tissue to the greater Marvel Universe, as well. While we don't see any of the Defenders, let alone the Avengers, in The Punisher, we do get another glimpse of the Dogs of Hell, the biker gang seen in Agents of S.H.I.E.L.D. and Daredevil. The fictitious outlaw motorcycle club was subsequently introduced into the Marvel Comics universe, as one of the New York criminal crews connected to The Kingpin.
Claire Temple isn't in The Punisher but audiences were treated to another regular from Netflix's MCU stable. Turk, the fan favorite low level arms dealer played by Rob Morgan, is once again in the wrong place at the wrong time. Thankfully, in a rare act of mercy against a criminal, The Punisher spares Turk, which means he'll be alive to potentially make appearances in new seasons of Jessica Jones, Iron Fist, and the like.
A few framed newspaper items in the background give us the show's biggest reminder that The Punisher takes place in the greater Marvel Cinematic Universe. Karen Page hasn't taken down two of the articles framed by her friend and mentor, the late Ben Urich, who used to occupy her office. One is about the green goliath's battle with Abomination in The Incredible Hulk and the other is about the alien invasion of New York depicted in The Avengers, which is the event that brought Daredevil's Hell's Kitchen back to the state of disrepair depicted in the classic Daredevil comics. There's a new headline to be seen as well, presumably written by the former legal aide herself: "CHAOS UNDER THE STREETS!" This is most certainly a reference to the events of The Defenders, which culminated in an underground showdown.