Oops! Just noticed I didn't get my quotation marks right:
Quote: 'Truss dedicates the book "to the memory of the striking Bolshevik printers of St. Petersburg who, in 1905, demanded to be paid the same rate for punctuation marks as for letters, and thereby directly precipitated the first Russian Revolution"; she added this dedication as an afterthought after finding the factoid in a speech from a librarian.[1]' Wikipedia
And, euh... maybe others have a tiny prob. with capitals. 
Your mother's got her work cut out, Mary, if she goes round telling people about all the similar mistakes on shop signs. But I think punctuation and capitalisation are the only "inaudible' parts of written English grammar.
I don't take this stuff too seriously - not like the French with their hundreds of rules for written French set in stone in the 18th century - all "inaudible". They spend as long at school trying to learn "correct" orthography (nobody succeeds 100%) as the Chinese and Japanese do learning characters and they don't even get the reward at the end of reading faster than we do in English.
By the way, I'm impressed by how correctly most people write on these forums. When I venture into other realms I realise that, though not unique, it's quite rare.
Cheers,
Glenys