It varies per individual. Contact comes in several forms. I don't have any from Satan himself that I'm aware of. I'm not certain what he'd want with simple ole me. However I can tell of a few. My guardian demon, whose name I don't know yet, likes to contact me through sensations like that of the physical feelings you get from emotions. And occasionally a touch on one of either of my shoulders for specific situations. Until I develop more I'll have to go with those and do good to interpret them best I can.
Marchosias, or perhaps someone who appeared on her behalf was the complete opposite of subtle. My first experience with her was her shadow darting around the room and the kitchen and giggling. It was so vivid I could even hear her hair rustle when she turned directions. The best part is I didn't even feel close to afraid. I felt excited like I was meeting a new friend. I'll cherish that memory even into the next life. At another time, I won't go into specifics on it, but she or someone under her turned the light that shone off of my candles blue. Whereas normally, an orange flame, emites orange light. Some tears of relief were shed that night.