In the US, we very commonly use cops to mean the police, so this should be accepted. A common story is the term originated in New York City in the mid-1800's when the mayor at the time decided the police would be more professional looking wearing uniforms that included copper buttons. I have also heard stories that is actually came from the London police wearing uniforms with copper buttons. So, who really knows where it actually originated. Nonetheless, it definitely should be accepted.