Macros located the the ImageJ/plugins folder, or a subfolder,
  and with an underscore in their name, are installed in the Plugins
  menu, or in the submenu that corresponds to the subfolder.
  Note that macros with a ".ijm" extension of scripts with a ".js"
  extension to not need an underscore in the name.

  Use the Plugins>Shortcuts>Install Plugin command 
  to create keyboard shortcuts to these macros.

  More information is available at:
  <http://rsb.info.nih.gov/ij/developer/macro/macros.html>