Question: I suspect that my site is penalized by Google.

Is there a way to check if it's true?

EDIT:
Webmaster Tools don't show any messages. Sometimes there are warnings about inaccessible (404, Soft 404s) pages on the site that come and go, and couple of warnings about duplicate page titles (in online documentation for my software), though.

Answer: 
Google will contact webmasters through their [Webmasters Tools](https://www.google.com/webmasters/tools/home?hl=en) page to let them know there is an issue with their site. If you don't already have an account sign up for one and see if a message is there for you.
Ok, I did read some other sites and I think I got the answer for my question.

If someone else is interested, following links have helped me:

* [How to Handle a Google Penalty](http://moz.com/blog/how-to-handle-a-google-penalty-and-an-example-from-the-field-of-real-estate) (contains good flowchart)
* [10 Ways to Diagnose a Google Penalty](http://www.searchenginejournal.com/10-ways-to-diagnose-a-google-penalty/)