Well, I suppose it could be to start a conversation...but...I always thought IF I were to get one, it would be more in the order of 'flying ones flag'...if you get the imagery. Art, or even simple words, can display, even to ourselves, what represents our inner hearts...what we wish to portray outwardly. Sometimes Christians do this by wearing jewellery, or shirts...I suppose tattoos would be the next level...and one you'd better be sure you'll like for the rest of this life!!
@Naomi25
Yes, I do take your point. I guess some would say that a desire to start witness conversations and a wish to 'fly one's flag' are really two sides of the same coin, so to speak, really, being all about personal testimony.
My wife and I talked to a young lady with the whole of John 3.16's wording tattooed on her wrist area; it was her favorite Bible verse and mine also; and I'm sure that other conversations have arisen as a result of her willingness to have it done.
I can quite imagine her having thought and prayed about it a great deal, spent time planning the placement and visiting parlors both to check out inking styles and artist quotes, and - indeed, as you say is very necessary beforehand - making sure in her own mind first of all that she wanted it for the rest of her life. Really nowadays it's not the preserve of people of radical, avant-garde tendencies to receive a bit of inking; as GodsGrace says it's now what really conservative young women and others do.
The picture below (I coudn't get it any smaller) may well reflect - even in the small size - what really is in the wearer's inner heart (like you say), and she might have reflected that what was in her inner heart was most definitely worth a sharp pricking for a very short time, for something permanent, if this makes sense?
tattooshunt dot com