"re:" followed by subject content.
There is no proper abbreviation for the word global. It is often symbolized by a letter G in acronyms. As far as an abbreviation goes, many people use Gl., but this is in no way a proper abbreviation.
there is no proper abbreviation for say but you can use: s. say. or sy.
The proper abbreviation for extension is "ext."
The proper abbreviation for kilohertz is kHz.
The proper abbreviation for Sunday is Sun.
The proper abbreviation for Registered Chemist is RCh.
The proper abbreviation title for an attorney is "Esq."
The accepted abbreviation is Depr.
there is no abbreviation
The proper abbreviation for the word "confirmed" is "conf."
Mr. is the abbreviation for the proper noun Mister, a title. Proper nouns are always capitalized, as well as the abbreviation for a proper noun.
You can use St or Ste as proper abbreviations for street in the English language.