DNA watermarking is a reliable technology for marking recombinant strains of bacteria, yeast races, plant varieties and lines, including GMOs. A DNA watermark is a rather short sequence of nucleotides inserted into the DNA of any organisms in order to prove its genetically engineered or fully synthetic origin. Virtually any non-biological information in the form of authors' surnames, places of their work, some unique texts, etc. can be encoded in DNA watermarks. Moreover, different authors use various methods of converting such non-genetic information into nucleotide sequences, briefly discussed in this review. In addition to DNA marker sites embedded in genomes, water DNA signs can also be considered as some unique nucleotide sequences added to various media and substances (groundwater, oil, milk, ink, pesticides, etc.), including chemically synthesized long oligonucleotides, which can then be detected using PCR. Some attention is paid in this review to the problem of GMO, which, in fact, should not exist due to many reasons, the main of which is that GM plants are no more dangerous than ordinary varieties of agricultural plants.