Hmm, I'm in the process of embroidering a whole line of onesies for my best friend who is pregnant, some with prominently displayed skulls. It honestly had never occured to me that some people would find it inappropriate. Oh well, back to the drawing board.
If you want the back to look nice, you must avoid knots at all costs! It takes a litte longer to start a new length of thread and make sure you catch it under a few stitches then trim, but weaving in the end when you're done I think is easier than making a knot. It just takes getting used to, but you'll never go back. I have done a lot of cross stitching and just started the embroidery thing, so it's weird to know the backs will usually be visible. Good luck!