This is a 24mm bronze button made by Hobson & Sons. I believe it is to the Tientsin British Municipal Police. It bears the Tientsin Coat of Arms and is quite similar in design to the button of the Tientsin British Municipal Emergency Corps which was brass and had a scroll with 'Tientsin 1900' under the main emblem. My apologies for my amateur photographs
If anyone has the helmet plates I would love to hear from them !