Hi Jpeg,
I'd like to add that Bf (capital B, lower case f) remained the Reichsluftfahrtministerium's (air ministry's) designation of the series, but Messerschmitt referred to the type as Me 109 (capital M, lower case e) after the change to Messerschmitt AG. At the same time, companies like Erla who were license-producing the aircraft, stayed with the Bf designation.
There are official RLM documents that refer to Messerschmitt's fighter as Bf 109 and Me 109 on the same page :-)
Me 109 was also used by the Luftwaffe's propaganda magazin "Der Adler" ('The Eagle'), and it could well have been this one that made the M-E 1-0-9 designation popular outside Germany: "Der Adler" until 1941 was distributed internationally, with each picture actually featuring a second, English caption for the American readers.
German pilots and groundcrew invariably referred to the aircraft as "Me 109" (in German use pronounced as "May Hundred-Nine") anyway.
By the way, the well-known subtype designations "Emil", "Friedrich" and "Gustav" were merely simply phonetic codes for the designation letter. The earlier Messerschmitts likewise were referred to as "Anton", "Berta", "Cäsar" and "Dora" - none of these were nicknames in the true sense, and could be applied for all aircraft types - "Dora" in particular rising to fame as the Fw 190D-9's name.
You might have noticed I typed "Friedrich" and not "Franz" - "Franz" was never used by the Luftwaffe since it was neither in the phonetic alphabet nor fit for inclusion, as it could be easily confused with "Hans" :-)
"Friedrich" could be abbreviated "Fritz" in everyday use, but "Franz" is a faux pas that in my opinion originated with Air Warrior, just like the "Niki" designation. Maybe even worse than "Niki", since the programmers called the Me 109F "Franz" in the actual plane selection menu!
Regards,
Henning (HoHun)