1. A method, comprising: receiving a search result; computing a hash based on an order of at least part of the search result to produce a bit sequence corresponding to the search result; performing a null hypothesis test that includes testing the bit sequence against a null hypothesis that the bit sequence was generated by a random variable with a binomial distribution with a parameter p=0.5; comparing a result of the null hypothesis test to a desired significance level; and determining that the search result was generated with a watermark if the result of the null hypothesis test is less than the desired significance level.