How to know if a web-site is developed/running in a Liferay Portal instance?

Since Liferay has a fully customizable appearance, I would like to know how is the best/easiest way to determine or identify if some web-site is developed or running under a Liferay Portal instance. I tried the following:

• Inspect the HTML source code returned by the server, and check if some Javascript objetcts like "Liferay" or "ThemeDisplay" are visible, or any css class from the liferay default theme... an example would be one famous site developed in Liferay http://ift.tt/mghTiA

Any further thoughts/ideas ?

Thank you ver much in advance