Thats the one! Heres the response I had on the UK forum
Hi Snetboy (Bob?) and welcome to the forum.
As you might already be aware Pepsi-Cola has a history going back to the late 19th century which is well documented on many internet sites.
Wikipedia gives a good basic...
First time using the forum and looking for help on ageing a Pepsi bottle I found whilst digging out an old hedge.
The bottle has a letter "R" in the middle of its base.
Bob (Norfolk, UK)