I have 100s of Bridgewater mugs collected over 20 years . There seems to be a lot written in these reviews about 'fake' Bridgewater mugs and the need to check they are genuine. I have never come across a Bridgewater mug being sold on ebay which hasnt been genuine. There are fake butter/cheese dishes but thats a famous story.
They do not all have a letter on the bottom. Some of the sponged or painted ones are signed by the artist (with initials) some of the lithos (the transfers) have a tiny litho letter on them. Many , many genuine mugs - especially older pieces have neither- just the Bridgewater stamp (which has had dozens of variations over the years) .
Occasionally Bridgewater mugs have been produced in different styles (straight up and down without the wider base) . These although rarer seem to sell for much less- possibly as they are not as attractive.
Very occasionally a seller claims a Whittards mug to be Bridgewater or possibly made by Bridgewater when they are not. In the very early days they did make a range for Whittards and those mugs are highly priced and collectable however those mugs were in the classic Bridgewater shape. If you look at a modern Whittards mug its a different shape from Bridgewater and so easy to spot that its not Bridgewater (wider deeper base- thinner handle) -if in doubt ask the seller for a picture of the base stamp.
The pottery cafe is where you can go and paint Bridgewater shapes (mugs, plates, egg cups etc) yourself. These are then glazed and finished by Bridgewater and returned to you. They are stamped pottery cafe and usually have a hand painted number (the reference number to get them back to you when they go in the kiln). As such they are not strictly Bridgewater mugs- quite a few turn up on ebay- mostly they say pottery cafe but not always- these are painted or sponged pieces- not lithos.
Seconds have an S scraped into the glaze on the bottom with a sharp tool (this often looks more like a z). Bridgewater sell seconds through their factory shop, collectors sales, village hall sales and at sale times through large retailers. The quality of seconds varies- some have pin pricks in the glaze, dirt from the factory roof, painting smudges, small faults in the litho, differences in paint colour, occasionally small chips in the china etc. Some seconds have faults which are very, very hard to spot (the fault is often marked with a china graph pencil when the item is first sold- this washes off). If in doubt ask the seller if it has an s scratched in the bottom and what the fault is. A new Bridgewater mug currently retails at £14.95 and seconds are usually £10.95 but can be a lot cheaper at sale times or if the factory shop has offers on a design. If you want a nice everyday mug to use then seconds can be a good buy however they would not hold value for collectors as a first would so it may be worth paying the extra to buy a first if you are looking for an investment.
A number of Bridgewater firsts- especially older ones (but I have quite a few new ones as well) have faults in them- its the quirky nature of hand made pottery. In my opinion Bridgewater quality control has become much stricter over the years - so they have more seconds.