How would I know if I have ink poisoning?

I'll bet you don't. If you are compulsively drinking fountain pen ink, more than an ounce at a time, you might get sick from it. You should get with somebody who can help you with this compulsion -- your personal physician has heard much stranger and won't think the less of you. If somebody told you to stop writing note to yourself on your hand, stop worrying, it won't make you sick.