This is going slightly off-topic, but found the following on United Glass' (that serves Diageo and Allied etc. with glass) homepage:
10. What are the numbers, letters and dots that feature on a bottle?
A: The base of a bottle includes a number of identification codes. Each bottle will incorporate some or all
of the following:
> The Punt Mark - this symbol identifies which glass manufacturer made the container - in UG's case, this is a miniature UG logo
> A plant identifier - a letter followed by a number identifies which plant made the glass - U8 shows the container was made at United Glass in Alloa, U0 means it was made in Harlow
> The job number - typically consisting of two letters followed by three numbers, this identifies the actual container
> The capacity - usually shown in millilitres or centilitres
> The fill height - shown in millimetres, this is the depth below the rim of the container to which the product should be filled
> The section code - a series of dots, this identifies the mould used to make the glass. Combined with the date and time code printed on the bottle after manufacture, this enables any glass to be traced back to the precise section of machinery and mould in which the container was formed.