Quotes on T-Shirts

What is the name of your state? Illinois

I am a Screenprinter working on a new line of printed tshirts for sell on my website and possably supplying these shirts to retail outlets.

What these printed shirts will consist of is comical quotes, just text no pictures. If pictures are used I will use originals from my own art department. Some of the quotes are from people that are no longer alive, so i should be clear on those, but some of them I can't find an author.

You see shirts like these in novelty stores and they dont have a copyright symbol on them while others do.
Should I give aknowlagement to the auther at the end of the quote?

I have some 'sayings' that I came up with on my own, but who really knows if someone hasn't already said it before.

Would I be in violation of copyright law if I print and sell these shirts with quotes of unknown authors?

If so could I possably put a disclaimer on my website saying that the customer is purchasing The shirt only and that the printing is added at no extra charge? Therefore Im not profiting from the quoted material.

If the statement is trademarked, or even copyrighted, you need the permission of the holder BEFORE you decide to use their property. If you don't, you could lose your inventory and all profits.