my son wants me to sign a home occupation permit so he can run a business on-line from our home. As the homeowner will I have any liability issues .

You will have all of the liability concerns which any property owner which allows a business to be operated therein would have, including potential alter ego liability and premises liability.  You should make sure that your son's economic relationship to your home is defined and that your son's business is properly authorized, structured, incorporated, capitalized and insured.