If you want to sign, it appears you can. The NY definition of RP is vague enough (as for most tax agencies) that if someone wants to get in on the fun, they can. Most tax agencies have a list of who is on the hook by law, and do not mind if others want to bite as well. The more they can seek money from, the better for the agency. FWIW, NYS came after me for employment taxes, based on a set of sample NYS-45 data which had our actual CA address, with the fake employees having a CA address, with invalid SSN's, unsigned, sent to their forms approval office. It is clear they have no issue coming after whomever they perceive as being liable.