We were always told just to wear the highest we had achieved; though I think technically you are only supposed to wear what your current qualification is (for someone who is out that would be nothing); but, I haven't read AR 670-1 in awhile and really don't feel like reading AR 670-1 for you right now because it sucks and is boring.
Just Google AR 670-1 and read, it SHOULD have the answer for you.
on a side note, I once saw an old, old gentleman at one of our 31st infantry military balls who was wearing his "Flamethrower" marksmanship bar, below his Expert badge. No one said a word about it to him, so I'm assuming you're probably good to go with whatever your highest was.