Want an OS X Service to convert a Pivotal Tracker story id or URL into a Markdown link? Create a new Service in Automator and enter the following in a Run JavaScript step. Save, give it a name, and you'll be able to select it from the Services menu.

PivotalTrackerMarkdownLink.js

/// Convert a Pivotal Tracker story id (#1234, 1234) or URL into a Markdown link using the story number as the link text.
function markdownTrackerLink(text) {
  var regex = /\s*(http.*pivotaltracker\.com\/story\/show\/(\d+)|#?(\d+))\s*/;
  var id;
  var groups;

  if (regex.test(text)) {
    groups = regex.exec(text);
    id = groups[3] || groups[2];
    return "[#"+id+"](https://www.pivotaltracker.com/story/show/"+id+")";
  }
  else {
    return url;
  }
}

function run(input, parameters) {
	return markdownTrackerLink(input);
}