I came back here on Bitcointalk from a very long hiatus due to personal reasons. I wanted to start offering again my services such as participating in signature campaigns but I don't know where to start. Can some tell me what are the current qualifications to join some campaign and how/where to get them? Any help will be appreciated. Thank you in advance!
You cannot expect to just returned and immediately get accepted into a signature campaign, you need to be active and have a quality post profile and having some merits will also justifies your quality contributions, this are what the campaign manager among other things they look at in selecting members to participate in their signature campaign, also you will have to read the campaign thread and see if you have the qualifications needed for an application before applying on service board.
They maybe look after the merits earned but they also look for other criteria such as on where the user post, how active they are posting and how long the interval they post since sometimes its annoying to see someone do post bursting.
Maybe for now since he just newly comeback in the scene he should not think about participating on any campaign but rather build his account back and earn all the pointers suggested by people here.