Unusual Markings on Cylinder Rim

[HayesGreener]

I am looking at a Model 10-8 heavy barrel with stamped markings near each chamber. I suspect these are proof house markings but don't know. SN is 99594. It also has external markings that make me believe it was a police gun. From the UK perhaps? Sorry I don't know how to post a photo since the photobucket bandits struck