I for one don't find it "offensive", just weird, but after the explanation it makes sence so it isn't that weird then, although I think it didn't needed a inverted cross to represent your name anyway, though that's just me.
Nothing means something once you give a meaning to it, so it doesn't matter if you have a knife, a horn or a drawn of a demon in any place, as long as you have a different intention by having it it shouldn't be offensive at all.
In what world is that a unfinished pentagram!? Lol, he's just a (word that starts with p and ends with y) so it's best if you just ignore him.