With all due respect to gunut, I have never come across a fake pin on an English gun but no doubt they exist.
The rule of thumb is that if there is a pin showing in the bar of the lock plate, it is a true bar-action lock. If not, it is a back action masquerading as a bar-action, sometimes called a 'back-action bar lock'.
At the risk of stirring up a hornet's nest, it is usually assumed that a back action is of lower quality than a bar action.
These people are ignoring the many sidelock O/U's and double rifles made by the best gunmakers in the world that very often use back action locks.
Although I will admit that a larger proportion of full bar-actions are of high quality than back-actions, it does not follow that a back-action can not be of fabulous quality and finish.
As an example I would offer up this McCririck:
http://www.heritageguns.co.uk/McCririck%20SLE/McCririck%20SLE%20Details.htm
and any number of guns by Blanch and Scott.