In referring to a local church, does the name "St Giles" require a period after the "St"? I was told that to add a period confuses it with the abbreviation for street.
US postal service official abbreviations for street suffixes actually do not include a period.– Mark BeadlesJul 24, 2012 at 1:34
I believe this is primarily a difference between American English and British/Australian English. American English usually includes the period (e.g., St. Patrick's Cathedral in New York or St. Paul, Minnesota) whereas British and Australian English typically omits it (e.g., St Paul's Cathedral in London).
To expand a little on Ben's answer, the British practice is not to use a full stop where the abbreviation contains the first and last letters of the word abbreviated. So, St (which can also be an abbreviation of street) but etc. That said, British style generally tends towards minimalist punctuation.
This rings true to me for St=Saint, but I skimmed through Google Books hits for "main st" and "high st" (I imagine the first ones are predominantly US, and the second UK). If there was a difference, I reckon British "High St." had the full stop more often (but they both had it more often than not! :). Jul 29, 2012 at 0:29
Did the search exclude cases where 'st' came at the end of a sentence and would thus have a full stop anyway? Jul 29, 2012 at 5:59
No (I can't see any easy way to do that). But I've no reason to suppose "end of sentence" would be any more likely in either US or UK contexts, but if I detected a slight difference (it certainly wasn't extreme, and may not have existed at all), it was for BrE usages to include the period more often. Jul 29, 2012 at 14:13
The Cambridge Guide to English Usage by Pam Peters (Cambridge University Press):
The shortened form St is normally left unstopped by British writers and editors, because (a) it's a contraction rather than an abbreviation, and (b) it contains a lower case letter. North Americans when using a saint's name usually punctuate it as St., as exemplified in the Chicago Manual (2003): and this style is carried over into placenames (e.g. St. Louis) in encyclopedic dictionaries such as Random House (1987) and Canadian Oxford Dictionary (1998).
2+1 for quoting that excellent book. The distinction between a contraction and an abbreviation is one worth making. Jul 29, 2012 at 5:59