Relying on UID is not the best idea. The trick with instance variable works very well.
In the example LaDestitute gave you actually check if the clicked object is the one you need. If you want to grab the instance directly from any place use the following:
System > Pick by comparison
first argument: spriteFont.instanceName
second argument: {the name you set manually}
Just be sure you have each instance name unique. Or it might be useful to have some of them named the same. For instance let's say you have a "credits" section in your game which is very long. You want to pin them to some drag&drop background sprite so user could scroll and see all the credits. Then you might set all the spritefonts instanceName value to "credits" and then pin them all with one event to the sprite.
So basically with the instanceName variable you can pick the distinct instance of an object or some group of them.