trademarks in united states police?
Police in the U.S. do not have trademarks.
If you're looking for police logos, here are pictures of many of them.
http://www.google.com/search?q=logos+U.S.+police&hl=en&noj=1&prmd=imvns&source=lnms&tbm=isch&sa=X&ei=AwoQUJCWOZTtqAGIhICwAg&ved=0CEYQ_AUoAQ&biw=711&bih=453