This is what you get for naming everything you love Henry. In their defense, he looks so sad locked up in the maze. On the other hand, they should have checked that the leash was long enough.
Lucifer (lower back): Perpetually his hand placement when they're near each other in an official capacity- guiding the 'human ambassador' to safely mingle during Diavolo's parties. The title may have started as a panicked joke, but she's taken it seriously every day there after. It was their secret for a while, but he did love to see his pact peek out from her dress when it was cut low enough to show. After a sufficient rise in status, it was seen as a mutual flex.
Mammon (left side of the waist): He originally wanted it to go on her neck, but reconsidered, wanting the location to be more "us" than "me". It ends up on her waist bevause he's always pulling her close- to dance, away from explosions, out of fights...
Leviathan (back of left ankle): unintentional and he found it super embarassing at first. He thought he didnt care about the placement, but something about an ankle seemed weirdly intimate. But he knew why it was there- he had lost his temper once, even worse than the TSL quiz, and when she had tried to run, his tail had wrapped around her ankle and tripped her, gripping so tightly that it fractured. He hated the memory, but came to love his pact on her ankle, almost like a legitamate tattoo.
Satan (upper left thigh): a natural placement, this is where he would put his hand to pull her closer when they read together. He liked to buy her dresses with high slits, allowing his pact mark to peek when she would cross her legs.
Asmodeous (low on right hip): Asmo has a surprisingly hard time getting her flustered, Carmafe seemingly invulnerable to his advances. While he was kind of happy and intrigued that she didnt flirt back, he wanted to fluster her really well, just once! He found this spot on accident, hand slipping lower than he meant it to. She was stumbling over her words, a blushing mess, and he'd give anything to see it again. And he did! When they found where the pact was placed she was stunned silent for a week.
Beel (tongue): Carmafe couldnt find or feel the mark, and it weirded her out but she ignored it, believing that Beel hadn't wanted a visible one. A week later she's eating sundaes with Mammon and Levi when Mammon started to choke. After he managed to not die, he squeezed her cheeks until she opened her mouth and they all saw the mark on her tongue. Beel didnt make any comment on it, but they could have sworn he was smirking as he walked away.
Belphegor (inside of left thigh): just kind of happened. Carmafe was too busy to indulge his every nap so they fell into a pattern where he would lay in her lap on the couch while she studied so voila- pact mark.