Arrow Season's 4 Big Bad, Damien Darhk, is so dark that the Green Arrow must learn to use the Light of the Soul to hope to defeat him. Darhk also wears very dark suits.
Even Battlestar Galactica has an obviously evil character: Brother Cavil, AKA Number One. A cynical, perverted old man who dresses in pure black, sometimes with a black hat, and takes pride in hating life.
While Buffy the Vampire Slayer isn't always black and white in terms of morality, you can't get much more Obviously Evil than the First Evil, an entity that is the source of all evil. The Master falls into this category too, like everyone who calls himself The Master.
The Source wears a black hood, carries a dark sword and is revealed to have half a face with tribal markings on it.
A strange case happened in the sixth season finale where the sisters found a parallel universe which was an evil alternative to their one (where the humans/witches were evil and demons were good). Their evil counterparts wore a lot of black leather and sported punk rocker hairstyles. Though they weren't as blatantly evil as most of the villains as they did join forces for the greater good.
Maaga in "Galaxy 4" is Obviously Evil from the get-go (despite the whole story subverting Beauty Equals Goodness in a very Anvilicious way), but the Doctor still runs off to commit genocide against the Rills on her word. Vicki and Steven, to their credit, are more skeptical.
Exaggerated in "The Power of the Daleks". Genre BlindMad Scientist Lesterson has rescued a bunch of Daleks from a downed space capsule who insist that they are his servants (in exchange for him powering them). The Doctor insists that they are evil, but Lesterson refuses to listen... until he observes them making Nazi salutes with their plungers and chanting "We will get our power! We will get our power!"
Most of the Doctor's moments of being cunning are when he's worked out that the man in Nazi-esque clothes who can't get through a sentence without scenery-chewing is obviously going to turn out to be evil, even though he hasn't done anything yet. For instance, the Second Doctor does this in "The Power of the Daleks" after noticing one of the characters has undergone an Evil Costume Switch.
None of the Atlanteans in "The Underwater Menace" seem to realise that Zaroff, the giggling Large HamMad Scientist with a ridiculous German accent who openly admits to wanting to blow up the Earth, is dangerous and totally bonkers, no matter what the Doctor says. In fact, he's so obviously evil that when the Atlantean Chief asks him how he knows Zaroff is bad, the Doctor is shown to struggle to articulate it in the manner of someone being asked to explain a ludicrously basic concept (he's reduced to asking 'have you looked into his eyes?' and pulling Zaroff-like faces).
Deconstructed (and this phrase used) in "Robot", when Sarah infiltrates a weapons development institute in order to find a mysterious robot the Doctor thinks is there. When she gets there a creepy and disdainful Mad Scientist makes the robot jump her, claims it was a joke, orders it to kill her, claims this was to prove it wouldn't, and then blackmails her. When Sarah returns to UNIT she tells the Brigadier that the organisation is "obviously evil" and they need to stop them. The Brigadier says that while he believes her, he needs more to go on than that he could lose his position if he goes in without due cause, and if they went through the red tape of obtaining the due cause the organisation would get a large advance warning and be able to clear everything up.
Davros in "Genesis of the Daleks" onwards. Nobody who looks like Emperor Palpatine in a wheelchair, shouts about extermination, and openly admits he'd destroy every living thing on the planet if he could just For the Evulz, is possibly going to be a good guy. Nevertheless, in "Genesis of the Daleks", both his own native Kaleds and even the racist enemy Thals who view Kaleds as subhumans openly trust him.
"Partners in Crime": Miss Foster comes across as a slimy diet pill conwoman because she is a slimy diet pill conwoman.
Subverted at the end of "Deep Breath". We're introduced to Missy, a woman who dresses like a Gothic Mary Poppins and gleefully says she runs Heaven. Nothing indicated her as being evil, yet most fans knew that there was no way she couldn't be a villain. Turns out she's the Master.
While not specifically on TV, a Spanish Class video series called En Busca de la Verdad (In Search of the Truth) has Turron, a man who dresses in a black trenchcoat, wears a dark hat, his face is never shown, and creepy music plays every time he appears. Nonetheless, most students laugh upon seeing him for the simple fact that he is so obvious. This is eventually subverted, however.
One of the criticisms of Aidan Gillen's turn as Littlefinger is that he's turned the character into someone who's obviously evil - not so much in a way that viewers can notice, but in a way that's so obvious even other characters should notice. Everything he says is coated in such a thick layer of malevolence that it's difficult to imagine other schemers not immediately suspecting him.
House Bolton's symbol is a flayed man. They're not nice people, to the point of often making the Lannisters look reasonable and friendly in comparison.
Aside from Roose Bolton's generally creepy mannerisms and eagerness to torture for information: Bolton is the Lord of the Dreadfort. Nevertheless he's much less Obviously Evil than in the books, and Benioff and Weiss carefully hid this particular lead in Season 3 both by greatly lessening Bolton's Obviously Evil qualities and established him more as a straight-up Colonel Badass and by making Rickard Karstark much more evil. And then came the Red Wedding, at which point both the Starks and the audience were likely underestimating his evilness.
The Queensguard under Cersei completely gave up the pretence of being White Knights, wearing black armour with black masks under their sinister helmets, and lead by a clearly zombified Gregor Clegane.
Euron Greyjoy, especially in Season 7 where Euron is dressed in black leather, has pitch-black sails, creepy eyeliners and somewhat pale skin, giving him a rather threatening appearance, not to mention that he casually talks about murder and violence in a gleeful manner.
Happy!: Very Bad Santa is a crazed, Christmas-obsessed child abductor. When Nick is tasked by the mob to team up with him on an assassination, Frank takes one look at him and instantly refuses, saying that he's obviously a complete psychopath.
In Merlin, one would think that someone would notice Morgana turning to the camera to give a comically evil grin every time she's on screen in Series 3...
At least with Morgana they have the excuse of not wanting to believe that she's become evil (Gwen appears to be have been in outright denial until it became impossible to ignore). A lot of the other villains, like Knight Valiant, Edwin Muirden and Cedric (especially once he's possessed) are so obviously evil it makes you wonder how Camelot stayed standing before Merlin came along.
A particularly prominent example is Lord Agravaine from series 4, who was so Obviously Evil that it greatly pushed the boundaries of suspension of disbelief that the rest of the cast didn't notice what he was up to. This rapidly led to him becoming one of the least popular characters ever to appear on the show.
Power Rangers isn't really subtle when it comes to villain designs. Every season of the franchise has at least one villain whose design just oozes evil.
Lord Zedd from Mighty Morphin' Power Rangers. He appears to be made of exposed muscles partly covered by gleaming metal skeleton-like plating; he wears long metal claws over the ends of his fingers; his face is a skull-like metal mask with a fang-filled Glasgow smile and the two eye sockets merged into a red, Cyclops-like visor; what appears to be his brain is exposed where his scalp should be; he has creepy plastic tubing with... something... flowing through it running up and down his limbs; and he wields a magical staff (that used to be a giant venomous snake) with a giant razor-edged Z on it. He is, in fact, bad.No, really?
Ransik from Power Rangers Time Force is one of the more nasty looking villains in the franchise. His suit has Spikes of Villainy, while the left half of his face is scarred with ulcers, which he tries to cover with a metal plate. His primary ability in combat is the manipulation of the bones in his own body, which he can turn into weapons. He is somewhat of a subversion, though, as he is not just a Card-Carrying Villain the franchise is known for, but rather a Knight Templar whose irrational hatred of humans fuels his deeds. After realizing his hatred almost caused him to kill his daughter, he voluntarily gives up the fight against the rangers, despite clearly having the upper hand against them.
Mesogog from Power Rangers Dino Thunder looks like a humanoid dinosaur with a black labcoat who talks in a scary low monotonous voice.
Show Me A Hero: Hank Spallone, the chief voice against the integration of Yonkers, couldn't look more sleazy if he tried. He greases his hair back, kicks his feet up onto his desk during city council meetings, and is always chewing on a toothpick.
The Borg in Star Trek. Not that they would hide their attitudes anyway...
The first sketch in That Mitchell and Webb Look has a Nazi officer asking his friend to take a good look at the skull badges on their caps and trying to work out if a skull emblem has ever been used in a non-evil context. (His friend tries for pirates, but while fun, they're still not good.)
"Hans... are we the baddies?"
The White Queen: Prince Edward of Lancaster possesses an emotionless, eerie gaze that displays his total Lack of Empathy. It's no wonder that other characters call him a monster.