Whenever Ive been pulled over by a cop for things like drunk driving checkpoints, I always lead with telling them, "By the way, I have a stutter, so if my speech is weird at all it's probably from that." Depending on the vibes I'm getting from the cop (I'm in a fairly small town in Canada so this might not be a good idea elsewhere in the world) I might even make a bit of a joke and say "I swear I'm not just blackout drunk or something and that's what's affecting my speech." So far every cop I've said this to has been understanding and appreciative. Most have said some variation of "oh don't worry about it, thanks for mentioning it, I figured it was something like that." According to a 911 operator that I know, they are trained quite a bit on talking to people with various speech disorders who call into 911, so I assume (again, Canada standards here) that police would also be trained on handling it properly. But more info is generally better