Modern molecular techniques don't really have to leave signs. Indeed scientists synthesised a copy of sars-cov-2 from the sequence data a few months after the sequence was published:

"it is possible for researchers to reconstruct the virus in a lab, using either fragments of virus from patients, or fragments of DNA that are synthesised chemically by biotech companies. " https://www.varsity.co.uk/science/19172

It seems you can basically type any sequence you want and have it made up.