The stylised lettering was produced from cast iron by Walter Macfarlane at their Saracen Foundry in Glasgow.
The variety of their output of architectural cast iron components was as extraordinary as it was prolific.
I was lucky enough a few years back to obtain a reprinted copy of a monumental 2-volume catalogue dating from around 1885 - a real eye-opener into a past age when cast iron was king.
The lettering was available in heights of 2, 2 1/2, 3, 4, 6, 9, 16, 20 and 24"!
I have not yet been able to identify the font used.
There is another example right under your nose Phil - just up from the Nutshell pub, high up on the facade of the former Post Office, which is currently undergoing redevelopment.
I passed it today and was fortunate to secure a visit - with appropriate PPE - to the 2nd level of scaffolding to photograph each letter: