Good morning afternoon, campers! Seeing this topic has finally persuaded me (after a long career as a lurker) to set up a username so that I can contribute something on station signs (not loco and rolling stock insignia, about which I know very little).
First, with apologies, I'm going to refer this thread to Pedant's Corner. A printer's typeface is a family of type of a particular design. In metal typesetting, a font was a particular size, weight and style of a typeface. (Thanks Mr. Google.)
Over the years I've amassed quite a collection of images and dimensions of SR enamel station signs. The staff of some well-known heritage railways probably thought I was casing the joint, but there was some method in it as I was aiming to get some replica signs made.
I quickly concluded that the lettering style used by the SR for its enamel station signs had been nowhere near a competent typographer. Many of the proportions look rather odd compared with, say, Johnson or Gill Sans - the R referred to by Nearholmer is a case in point - and there is considerable variation in detail between examples and between manufacturers (there were several). As a general rule the weight seems to have become lighter as time went on. The patterns for the individual signs will have been made by hand and my best guess is that they started off by replicating signwriting practice, possibly from a pattern book. The pointy ends were probably easier to cut out.
The SR muddied the waters after WW2 by producing some 18" x 6" dished door plates with a much finer, nearly-but-not-quite-Gill-Sans, version of the style. These are frequently mis-described as BR plates by the railwayana trade.
There were a couple of exceptions to the general rule. First, there was an early, very heavy version of the lettering with squared off ends. This is not common but the Bluebell has a couple of examples from West Hoathly on display. Second, enamel poster headers used an outlined version which initially had rounded ends but later (probably in the 1930s) changed to pointy ends. This was also used for the "Southern Railway" title on posters.
I hope that's of some help. The best advice I can offer to anyone trying to model these signs is to find an original which dates from about the time you're interested in and copy that. Heritage railways are a good source of inspiration but beware! There are a lot of modern replica signs about which may introduce their own little variations...