How do I add a directory of class files to my Maven project?

I started a Maven project to build a Vision component for Ignition. I intend to use the integrisign library to capture input from a series of ePad signature tablets.

The SDK consists of a folder called ‘integrisign’ that includes a number of class files. I use it in my java code by importing it:

import integrisign.*;

As long as I have the integrisign folder in my Maven project folder then the command mvn package finds it and builds the modl file without issue. But then when I install the module and try to use it in Designer, the console shows the following:

Exception in thread "AWT-EventQueue-0" java.lang.Error: Unresolved compilation problems: 
The import integrisign cannot be resolved

I’m not experienced at all with Maven. I feel that I have missed a step in the configuration of the project. How do I tell Maven where the class files are so they can be built into the modl file? Or have I missed another important step?