1. Contact the Procuratorate: You can try to contact the local Procuratorate, explain the situation and request its signature. If the contents of the investigation report are true and reliable, the procuratorate may assist in signing it.

2. Contact other authorized departments: You can try to contact other authorized departments, such as the Public Security Bureau, Work Safety Bureau, etc., to request their signature. These departments may have interests and responsibilities in fire incident investigations, and signing the investigation report may enhance their legitimacy.

3. Contact a lawyer: You can consult relevant legal professionals or lawyers to find out whether there are other legal solutions. It should be noted that no matter what method is adopted, the authenticity and legality of the investigation report should be ensured. nature, and comply with relevant laws, regulations and procedural requirements.