I always recommend businesses register their trademarks federally; doing so provides many advantages over relying on common law protection. However, it sometimes happens that a mark or a logo slips through and a competitor begins diverting trade by using a similar name.
Arizona provides a number of common law vehicles that the courts often confuse and conflate: trademark infringement, misappropriation, palming off; they all fall under the umbrella of unfair competition. They also all revolve around the same central idea, that a competitor tried to steal business by passing off its products as yours, either by copying the product, applying your name or logo, or some other method. Most importantly, realize that these doctrines are governed by equitable principles, which means, basically, the court can decide what is fair. If the equities fall on your side, you should be able to get an injunction; attorney’s fees are going to depend on the exact nature of the claim.
The Lanham Act – the group of statutes that define federal trademark law – provides some protection for you if you never registered your trademark. Section 43 creates civil liability for anyone who uses in commerce a mark that can or does cause confusion as to the source of the marked product. The Lanham Act is another arrow in the quiver, but you won’t be able to use it to get your attorney’s fees back.
So, bottom line it. Register your marks with the USPTO for the greatest protection. If you don’t obtain federal registration, register it with the state – it’s cheap and easy. And lastly, if you still take neither of these actions, at least display your mark with the TM superscript. The notice that your TM symbol provides will weight the equities slightly more in your favor.