Legal analysis: unsigned resignation letters can be used as evidence of labor disputes, but in addition to resignation letters, evidence such as labor contracts, attendance records, payroll and social records should be collected to protect their own interests.

Legal basis: Circular II of the Ministry of Labor and Social Security on matters related to the establishment of labor relations. If the employer has not signed a labor contract with the employee, it may refer to the following documents when determining that there is a labor relationship between the two parties:

(a) payment vouchers or records (payroll), the payment of various social insurance premiums;

(2) Work Permit, Service Certificate and other documents that can prove the identity issued by the employer to the employee;

(3) Employment records such as Registration Form and Application Form filled out by employees;

(4) attendance records;

(5) Testimonies of other workers, etc.

Among them, the relevant documents in items (1), (3) and (4) shall be borne by the employer.