ReSharper 8.0 Web Help

ReSharper is able to validate string formatting methods, but in order to do so, it needs to know that a particular method takes a format string as a parameter. With standard methods, such as String.Format, Text.StringBuilder.AppendFormat, or Console.WriteLine, it is fairly obvious, but when a custom string formatting method appears, you have to tell ReSharper to interpret it as such - otherwise, here's what happens:
Apparently, in this case ReSharper wasn't able to make sure that all required arguments were passed and didn't warn about a missing argument.

To make ReSharper aware of a custom string formatting method
  1. Reference ReSharper code annotation attributes using either of two methods described in Code Annotations.
  2. Annotate your custom string formatting method with the StringFormatMethodAttribute attribute, which takes a single argument - name of format parameter as a string:

ReSharper will now be able to warn you about missing arguments when this custom formatting method is invoked. Even more, the Add argument quick-fix will make it easier for you to insert them: