The "P" name was earnt by producing songs and uploading them. Due to the main crowd behind Vocaloid Master being also fans of Idol Master a lot of entraints would go onto get the name "-P". But the thing is, you had to *earn* the "P" as it was taken as showing off if you didn't. In short, this is not how it was done.
Usually by the time you had a couple of hundred followers you had a name based on your uploaded content. Some producers even in Japan refused to use the "P" name they were given while others decided to go with it.
Its not used so much now either and its hard for westerners to earn it correctly, the guys at VO forum used to mock the wiki because we put up the correct details on the "P". But as a westerner its generally fine not to use "p".