Yes, it is illegal. According to Article 52 of the Chinese Trademark Law, if an unregistered trademark is passed off as registered, or if the use of an unregistered trademark violates Article 10 of this Law, the local administrative department for industry and commerce shall order cessation of the illegal act, demand rectification within a prescribed period, and may issue a public notice. Where the amount of illegal business revenue exceeds 50,000 yuan, a fine of up to 20% of such revenue may be imposed. Where there is no illegal business revenue or the amount is less than 50,000 yuan, a fine of up to 10,000 yuan may be imposed.