textfan The © symbol shows that the original writer has exerted their rights to be recognised as the author of the work - it is there as a reminder, if you like. In a book, on the imprint page, it shows you who the © holder is and it may not be the author of the work.
For example, on MN, we assign © of our threads to MN in the ts and cs so they can reuse them as they wish without paying anyone anything, so MN, as the publisher of the 'work', is the © holder.
You don't have to use the © symbol for something to be copyrighted and you don't have to 'do' anything to © something. It is a given and as long as the author hasn't signed away their rights and they (or a company) are identified with the work, then a permission should be sought.
Even after the death of the originator, the © can be renewed and held by the estate (see above). As slowshow mentioned above, fair use does not apply if you are using the quote for commercial reasons.
So, OP, the bottom line is that you still have to apply for a permission from the © holder so do keep this in mind, OP, or you could be on the receiving end of a lawyer's letter if you quote something that's not in the public domain (i.e. free from ©) . To give you an example of something in the public domain, most nursery rhymes are not ©, but there are some exceptions. My advice would be if you are in any doubt at all, don't include it!
Good luck with your business, I hope it works out for you!