Rivan (he completed Rashi's commentary after he died starting on 19B) in Makkot 21a, commenting on the phrase, "וכתובת קעקע לא תתנו בכם" writes:
He maintains that R' Shimon ben Yehuda in the name of R' Shimon's position is only in regards to one's liability to receive מלקות. In other words, all forms of tattooing are forbidden but only tattooing the name of an idolatrous deity makes one liable to receive מלקות. It is unclear to me whether all would agree with Rivan's inference. Do we apply the terminology of Hilchot Shabbat here and say that aino chayav, or patur, implies that there is an issur? If so, then why is it that this terminology is given special attention and definition in Hilchot Shabbat - to clarify that patur means patur aval asur? I am sure someone must discuss this. Anyone have any ideas?