I got the Idea for River's Tattoos from an artist called savysami. You should check out her art, it's really good!

"Which one do you want to start with?" Penny looked at his chest, "This one?" She placed a hand directly over his heart, where the Hufflepuff crest sat. River chuckled and said, "I don't think I need to explain that one." Penny smirked, "Maybe not. But why here?" River shrugged. "Because in my heart, I'm a Hufflepuff." River sighed and said, "The rest, they're all adventures I've been through. This one," He traced a finger along his right collar bone where the words 'House Prefect' ran, "I got them at the beginning of our fifth year. This one," He traced his finger on his other collar bone, "I got them after the sunken vault. 'Always Remember, but never forget.'" He moved his hand to his left abdomen where a medieval Knight helmet was, "I got this one after I completed Sir Cadogan's trials. He was pleased when I showed him." Penny giggled and River smiled. "And here," The right side of his abdomen was a dragon sleeping on a pile of gold, "I had this one when we had to deal with that 'Dragon's treasure' stuff." He moved his hand to his sternum and said, "And this I got after the All-Wizard Victor event." It was a tattoo of the cup he had won during that time. He turned around and showed Penny the tattoos on his back. "I can't really see back there, so just touch the tattoo and I'll do my best to tell you what it is from memory." Penny nodded, "Alight. What's this one? It's… glowing." She gently placed a hand on the left side of his back and River chuckled. "That's my Patronus; a Unicorn. I had to use some extra enchantments to get it to glow the way a Patronus does." River felt her hand slowly move across his back and he did his best not to gasp or flinch. Merlin's Beard, that feels weird. Never had anyone touch me there before. "Is this the mirror of Erised?" River nodded. "Yeah, I got it after that whole goose chase for the bleeding thing. It was a friendly competition, and I got to spend time with my friends so I thought it would be nice." She placed her hand in between his shoulder blades, "And this is your Quidditch tattoo?" River smirked. "Yes. I can't really see it well, unless I stand in front of a mirror, but I don't often do that. If I remember correctly, it should be a Quaffle in between my shoulder blades, and two Beater's bats on each shoulder blade?" He heard Penny laugh and she said, "Flying colours. I mean, you got the tattoo so I would think you know what it looks like." She took her hand off his back and asked, "Is that everything?" River shook his head and turned around, and showed her his left arm, where there were three names written in elegant letters. Jacob Knotts, Penny Haywood and Rowan Khanna. "Jacob's name was the second tattoo I got. Then after Rakepick killed Rowan… Dumbledore said the dead never leave us so long as we remember them in our hearts. So I had my own little tribute to him." Penny underlined her name on his arm with her finger. "When did you get this?" River blushed and said, "It was the third one I got. I mean, well, I got it with Jacob's name. At the same time." River waited for her response with anxiety. "Is that when you got a crush on me?" River shook his head. "I've liked you since day one. But, after we did the Animagus process, it's when I actually realized it." Penny smiled at him, "Me too. After that whole thing, I realized how good of friends we are. Besides," she gave him a sly smile, "I like it."