Are Tattoos REALLY a Sin-greater or lesser, & if so, then why?

If it really is a Sin, I'd like to know more references than what's in the Bible, in Leviticus, 19:28. Some people believe in big sins and small sins, some people say that tattoos are a form of "mark of the Beast". Is it about where a tattoo is located on the body? Is it about what type of tattoo it is? My teaching states it's because of the Mosaic leprosy laws of the time in that region, so it wasn't a good idea to do anything involving purposely opening the skin: Please tell me what you heard, and/or what you think, THANKS!