People was amazed when i wrote my first Facebook status with the "via Nokia N9" tag, and maybe they still 'til now.
From what i know, since Facebook exist and Nokia had an internet phone (or vice versa ), N9 is the only phone that Made by Nokia that has unique signature on Facebook and Twitter.
"Because its connected with free advertising or something...."
Apple (iOS) has it, Samsung (mobile) has it, Android (Android) has it, Nokia (Social) has it....., its common from marketing side imo.

You should proud of it, or else, use Opera Mobile, Firefox, Snowshoe or Helium Reborn, they will gave you standar "from Mobile" tag.