ACCESS TO THE FULL FORUM FEATURES
Full Member is 120, of which gives you access to the complete forum features, such as posting images, wearing signature and avatar, e.t.c. So that makes the number 120 unique and important on the forum because without that these features can’t be access.
You don't need to be full member to post images as there are two options for the same like first one is you need to be junior member which requires 30 activity and only 1 merit and it will take more than month of active posting to reach that activity level and second one is going through Copper membership that usually projects that want to advertise on the forum go through.
So for signature campaign they are mostly for Full rank and above ranks but yes there are some for junior members also but the difference is signature space so you can't say it as restrictions.The number 120 is not distinctive as per my knowledge.
REQUIREMENT FOR CAMPAIGNS
Another place this number 120 plays a big role on the forum is when it comes to campaigns, because to most campaigns, one basic requirement always needed to join has always been, how many merits were you able to gained within the past 120 days. That is, now using the number ‘’120’’ as now a timeframe for measuring one’s eligibility with reference to merit earned.
That's right as most of the signature campaign has the requirements of specified earned merits in past 120 days as it helps you to evaluate the performance of members as if they have managed to earn merits over four months of period or not.Not too much focus for 120 days as you are specifying.
USERS FORUM STATISTICS
This is quite another way the number 120 plays a role on the forum, because as an active forum member, a user’s account statistics is always given in reference to the past 120 days, which gives a summary information about the user’s performance, merit sent and received within that period of time.
Mostly the forum statistics are for 120 days for every user but you can check them for more days also as it's available on
https://bpip.org/ for each member you can check for.There are profile information for the forum members you can check past 120 days also so this is not correct also.