Okay this is a weird question.. how do you NOT remove pen ink from a white t-shirt?

so today i went to the JDRF diabetes walk with a group from church and they gave out t-shirts which we all wore. one of my friends wanted to write on the back my shirt so i said fine go ahead, then of course somebody else wanted to and from there everyone went crazy signing my back. i really lke all their autographs on it but the problem is they all signed with a regular pen, and i'm afraid that if i wash the shirt, the signitures will wash out. does regular pen ink wash out in the washing machine? or does it stay on like sharpie? do you think the writing will wash out or fade if i try and wash the shirt?