Pretty much any word/words can be trademarked of incorporated in a trademark. Others have pointed out a number of city names that have been used as trademarks.
The question of infringement comes up when similar names are used for similar goods/services. Your use of Dallas in the automotive filed would not infringe on the trademark โdallasโ owned by Lorimar in relation to their long running soap, the trademark โdallasโ owned by Dallas Semiconductors, or any of the other dozen or so trademarks โdallasโ registered with the USPTO that are not related to automotive goods or services.
It might infringe on federal trademarks related to the automotive industry or trademarks in your state of business. And, of course, there's the whole rest of the world to consider. No doubt there are a number of companies out there who have a legitimate trademark interest in โdallas autosโ. The question is do you have an interest as well which does not infringe on their exclusive rights.
If the question is whether the city has rights to the name then this is simple a question of looking up the term in the appropriate trademark databases to see if they have one. A city is basically treated no different than any other corporation. If they haven't bothered or been able to obtain a trademark then they have no exclusive rights to it. If they have then they do.
One city who won a UDRP for their name was Barcelona.
http://arbiter.wipo.int/domains/decisions/html/2000/d2000-0505.html
But that's not the end of the story. Even though Barcelona got their name through the UDRP the original registrant subsequently sued them in the US and got the name back. The reason given was that although they had a trademark in Spain they had no trademark in the US.
There is no clear cut yes or no to a generic question such as โare cut names trademarkedโ. You have to look at each name on an individual basis and consider a number of variables.
