Some people use house mounted flag polls. Here's a site showing what they look like. Biggest problem is to make sure you can keep an eye on it so someone does not walk off with it. Or, put it on a second floor. Besides he UK flag, you can get any number of message flags to use with it, if you have never heard about that. Hope this helps.
http://www.anyflag.com/flagpoles/flaghard.php
Depending on jurisditcion and/or city/state policy, police are considered on duty 24 hours a day. They must wear firearms everywhere they are unless out of state, and even then most carry their firearms with them.