No one knows but Steve is an honorary member of the Hellfire club.
It all came to be because Eddie received a memo stating that every club had to have a minimum number of members and his club was lacking one, meaning that if he want the club to be kept by the school board he had to find another member or close the club.
Eddie knew that if they were closed, they would never be able to open it up again even if they had many more members. It was not lost to him that even more students and parents thought they were some satanic cult or something, so he set himself the mission to find someone who could, at least, lend their name for the cause.
It kind of fell on his lap when golden boy Steve Harrington came looking for some pills to deal with his headaches. Eddie told Steve that he would discount some if he could do them the favor to sign in. Steve obviously rejected the idea, but if Eddie was known for something was his charisma (and power to insist on a matter) which finally made Steve caved and agree to do it, with the condition that it would only be his name and no one could ever find out he was in the club. Eddie accepted and even joked about the club also not wanting to have anything to do with Steve's name.
The next day, Steve went to the secretaries office to sign in to the club with Eddie coming with. The only acknowledgement of the deed was a casual nod that the hellfire members gave Steve when he came out of the office and nothing more.
And well, Eddie really intended to keep his promise, if it wasn't for another mandated rule he find out later. Every member of the club had to appear and be listed on the yearbook's page and photo. Which, sucks, but it had to be done. Eddie pleads again to Steve to come to the photo session (and wear the hellfire t-shirt) but Steve is adamant that it would never happen. This goes on for a whole week, Eddie following Steve asking him to make an appearance and Steve reminding him of his promise to only use his name and nothing more.
Once Eddie realizes Steve is serious about it, he is defeated and is ready for the club to be closed.
The day of the photoshoot everyone's mood is on the floor, this is the end of it, some are angry at Steve and the others are just down that they will be closed for a technicality like this. The photographer comes in and install the camera and just when he is directing them to the frame, to the surprise of everyone, Steve appears and without futher ado hurries Eddie to give him the "stupid t-shirt". Steve makes Eddie and everyone in the club to promise to keep his face out of everyone's yearbook one way or another and they comply.
When the yearbook comes out, everyone at school is shocked to see a page blatantly ripped out of every copy. One would think this was going to be reported or took to the principal but when people realized the missing page was about the Hellfire club, everyone took it as a blessing more than an attack. Aside from that, the only other proof of Steve is his list of extracurriculars but, has such a long list that the Hellfire club name is buried between the names. Leaving any trace of his involvement completely erased.
At least everyone thinks so, because there is a copy of the yearbook with that page intact and it's tucked securely in Eddie Munson's trailer.
That is until Dustin finds it out the day he comes to help Eddie and Steve move in together. He starts skimming through the thing when he spots the page and his eyes bulge when he sees the main photo. He has to read the footnote to really get that Steve Harrington was indeed a member of the Hellfire club and it's not a figment of his imagination.
Needless to say, Dustin spends the whole dinner asking questions about it while Steve is sending daggers at Eddie for keeping a copy without telling him.
