1) You can absolutely use a city name in your company's or product's name, such as "City Name Radiator Repair."2) Unfortunately, anyone else can do the same. You cannot trademark (and service markes function like trademarks in this regard) a descriptive name, and if you are selling radiator repair services/products in City X, it is absolutely descriptive to call the product or service "City X Radiator Repair." You need a name that's NOT descriptive to protect--e.g. if you live and sell in Dallas, calling it "New York Radiator Repair" would not be descriptive. So again, a very logical, obvious descriptive name or the common variations thereof are not protectable.3) City crest or shield: best thing to do is to check with the city's counsel or legal dept. While all federal material (pretty much) is in the public domain, I believe that states and their subunits (e.g. cities) have disction to copyright material. Best to check to see if you'll have trouble.