Because trademark rights in the United States on a first to use basis, it is important to document the first date you use a mark. This may be done by taking a dated photograph of the goods bearing the mark or keeping the original advertising if it shows the date the ad ran. You should also keep records of the first sale of goods or services made using the mark. This may include a bill of sale or invoice. If you do not have a dated photograph or advertisement, you might want to notarize a statement on the back of a photo or ad such as "This photo was taken on 12/31/98," or "This ad was placed on 12/31/98." While this provides perhaps less convincing evidence than a dated photo or ad, it is far better than a photo or ad with no date.