Oh god don't even get me started on this topic I live in a pretty nice suburban area and the LEO's are always out looking to catch people for the silliest reasons. My fellow cachers and I have had several run in's withe cops out here. So far 1 out of 5 know kinda what it is and of course we always get bugged by the 4 that dont. It seems there are a lot of caches in business area's with security and a couple of 25-28 year olds poking around with flashlights never looks good.
We have only ran into one cop who had heard of it and was very interested in the details of caching. So him and his partner pulled out there mag lights and helped us grab one from underneath a booger. That situation was cool, but I wish I could say the same for our most recent LEO story.....So my buddy p72pi went to go grab a cache in our local town. He drove up to a business build on a Sunday night around 10pm and as soon as he got the gz (booger) and pulled out his flash light 3 cops pulled there guns on him and tackled him to the ground. Turns out a silent alarm had just went off when he arrived and the cops thought he was breaking into the building. He tried to explain that he was geocaching and even showed them the cache and the app on his phone, but they thought it was a cover up story. After an hour of holding him there to sort everything out the cops finally released him say "if it wasn't for the evidence on your phone (geocaching site) we would have taken you to jail on the spot!" Now that really makes you think twice about how dangerous this game can be in certain area's.
To the OP, yes I would recommend a geo sticker for your car or better yet, a Geocaching.com t-shirt so support your story. I myself have a TB decal on the back window and a small geocache symbol on the side rear windows. I have always thought that most cops would know about it, especially where I live because the game is HUGE in this county/town. Infact the 10 anniversary took place in my town back in March of this year.