In Medieval Christian Europe, generally speaking, tattooing was banned in accordance with the Biblical laws in Leviticus against marking the skin. People with tattoos were usually seen as pagan. The 10th century Arab scholar Ahmad ibn Fadlan wrote an account of an apparently startling encounter with a tattooed Scandinavian covered from nearly head to foot in ink.

That being said, some medieval pilgrims received small tattoos to mark their arrival in holy sites, especially Jerusalem. Though the practice was not wide spread, it was generally seen as a meditative act of sacrifice to commemorate the journey.

For further reading, try Mordechay Levy, "Towards a History of Jerusalem Tattoo Marks among Western Pilgrims"

'Medieval Europe' is a huge time and space. Could you be more specific?