I try to print my name, first and last, legibly on the bottom of each piece, with a ball stylus, or use a nice stamp that I got from Jet Stamps. On bigger pieces, like plates, I try to add the name of my town. Not the date, but when first starting out I did put the date. A couple of months ago a lady emailed me and said she thought she had one of my mugs. It said "sylvia92" on the bottom. She bought it at a yard sale in San Francisco, and it had been her favorite mug for years. I live in Kansas, so I told her I did not think it could possibly be mine, there are a number of other potters with the same first name, some who live in California. She sent me a picture of the bottom, and sure enough, it was my signature. I can't imagine how she found me with just that much info, but she did. The mug broke and she wanted another one.
Also, I had a pretty nice pot sitting on my shelf for five years without a signature. Many, many people looked at the piece and almost bought it until they noticed it wasn't signed, then put it back and bought something else that they didn't like as much but had a signature. Finally one lady came in with a sharpie marker and asked me to sign the bottom, then bought it. So signatures do matter to customers.