(Some context: She likes him, they are in the car, she's in the back seat, he's in the passenger's seat. What's the best word for meaning she touched him trying not to make it too obvious?) “What is that necklace?” she asked. “My mother gave it to me when I was 15,” he told her. “What does it say?” “There is a Chinese inscription of well wishes.” He reached for the medal and handed it to her. She took it, inconspicuously stroking his hand and naked shoulder. What a treat.
I'd probably choose "casually". "inconspicuously" works, but it tells me that he didn't notice at all. I'd use it in a sentence like, "She inconspicuously slipped the necklace into her pocket." With a touch, he's bound to notice, even if he doesn't acknowledge it. To say that she did it "casually" says to me that she acted like it wasn't a big deal, which draws the least attention to it. Of course, if it's not him that she's hiding the touch from but whoever's driving the car, then "inconspicuously" could be the perfect fit. As with everything, it depends on the full picture. Choose the word that best fits your style and the meaning that you're trying to get across.
I was going to suggest casually or 'accidently' but both your suggestions would work in that situation.
From whose point of view is the story? Hers? Perhaps you could choose "lightly brushing" instead of stroking. The stroking part seems far more deliberate, whereas if it was a case of her trying to get away with an almost "accidental" touch, the brushing would make more sense. Just sayin.'
You win a cookie for asking the question that needs answered before the question can be answered for certain! If it's his POV, then it's odd that he's casting the judgment in the moment that her stroke had be inconspicuous, as he's probably actually thinking about what a treat it is, not her motivations. So I'd concentrate on describing the action (not the motivation for the action) and then having his reaction, which will give the reader all they need to understand the moment. If it's her POV, then I'd almost say be more deliberate, some thing like how she relishes the chance to sneak a feel (deliberately using terrible language so I don't write the scene for you, lol). Make it so her motivations, since she's the one seeming motivated to execute this action, are perfectly clear, and inconspicuously doesn't seem precise or telling enough. If it's an omni pov, so you're just reporting on the action... well, then shrug, I guess.
Thanks for your advice. Regarding here intentions: 1) It was very deliberate, but 2) She wanted to make it look casual to him, indeed, but not completely casual, a teeny, tiny bit of a hint, because she liked him. (Regarding POV... you caught me Meaning, I modified a bit the language to ask the question, so I should have removed the "what a treat." But yes, the comment is from her point of view.)