From wikipedia:

Although FAILE’s style can be located in these art historical legacies, their style and idiosyncratic vernacular make FAILE’s work distinct and recognizable. During the early years of their career, influenced by contemporaries Shepard Fairey, BAST, and WK Interact, FAILE generated both a process of assemblage and urban circulation, and consistent visual cues and themes. One such example is the Challenger spaceshuttle, which crashed shortly after its launch in 1986. Not only does the shuttle appear in various forms in much of FAILE’s work, the year “1986” is appended to their pieces as a signature that both invokes their specific use of the shuttle image, and also a reminder to their audience of the event itself, of its role in their personal history. “1986” is both indicative of a populist or dialogic impulse in much of FAILE’s work, and also an example of the characteristic ambivalence or dualism in their practice.[3] Recurring themes of binaries such as love/hate, peace/war, triumph/calamity, satiation/desire are all prevalent in work that seems to assimilate the global urban landscape but tenders only oblique opinions about that landscape.

Artists eh...?

One of the Patricks talked more about it in this interview a while back.

faileforum.proboards.com/index.cgi?board=failenews&action=display&thread=1612

maybe they have some relation to the event. could they of had family or were they there? etc. i dont think its in ill taste.

When I was at the Post No Bills show in July this came up. Before I attended the show, I knew very little of the duo other than seeing their prints, and a few pics from shows. Infact, I didnt realize it was a collective, until the Bedtime Stories show. I asked about the 1986, not really understanding why they signed all of their work that way, and the various repetition within the images. Anyhow...I was told that the events above had a pretty significant impact on both artists, and that is part of why they pay homage to both the year and the event. I dont think its in ill will, but rather something that impacted both.

And according to the interview above:

You sign your work 1986, which is a reference to the Space Shuttle Challenger.What is it about that disaster that makes you want to incorporate that into your work?

It’s kind of an off-spirit answer but in the beginning 1986 did come from the Challenger disaster. We were talking about putting things up on the street that you would see and connect with. For instance, you look at a piece of graffiti and you see and read it and that’s about it. We did this Space Shuttle Challenger going down with flames on it and had ‘Challenger’ written below it. The idea was “Oh Challenger” but there would be a secondary reaction, possibly with the person you’re with, “Hey, do you remember where you were when the Challenger disaster happened.” And then a whole host of stories would come up with people’s different experiences. It’s the idea that the power of a graphic can transport you back to a memory.

I think the above reply sums it up for me