It is always advisable to put a patent number or a patent pending on your products, once a patent application has been filed.
Why?It educates the public that there is protection applied for or that there is a protective right in force. More importantly, it warns potential infringers to be cautious about copying. Products with clear protection indications are less likely to be copied, and lawsuits against infringers are more likely to succeed.
ExampleThe Legaignoux brothers are the inventors of the inflatable kites, which was a true revolution in water sports. These inflatable kites could be relaunched from water, without the danger of loosing the kite, or worse the danger of loosing your life altogether. In 1985 they have filed for a patent and after their patent being filed and granted, the inventors have searched for and found numerous licensees.
|Figures from the EP0202271 European Patent for tube kites.|
|Patent marking on one of the original R3, one of the early Naish kites, designed for kitesurfing.|
Since then more than a million kites with the Legaignoux technology have been sold globally. Quite a success!
|Number of tube-kites sold annually, the arrows indicate the start and expiry of the|
first patent on tube-kites. the Numbers originate from various sources [3,4]
Without protecting and licensing, and without informing potential competitors, the two brothers and inventors would not have had such a profitable return on their truly lifetime investment. They did contribute to the world by introducing a new and exciting sport. And they created a global market now worth over 321 million US$ .
To all innovators: indicate the protection on your products well!
References and sources: About the inflatable kite: http://inflatablekite.com
 About the history of kite surfing: http://www.inmotionkitesurfing.com/2013/history-of-kiteboarding
 SBC Kiteboard: http://fksa.org/showthread.php?p=50397
http://www.sbckiteboard.com/news_article?news_id=2206 [available as link only in the internet archive, numbers are still available]
 Wikipedia: https://en.wikipedia.org/wiki/Kitesurfing