data-searchingattributes to your already working jQuery UI autocomplete field.
<input type="text" data-autocomplete-source="/path/to/ajax/results" data-hint="Type in a search term" data-searching="Searching" />
That's it! Refresh your page in your web browser, and you should now see your autocomplete field providing hints when you focus on the field or when it beings searching for matching values.
I encourage you to contribute improvements! Fork a branch on github, and submit a pull request to have your changes reviewed for inclusion.
jQuery UI Autocomplete Hint extension is released under the MIT license.