Dear Jim,
Allow me to chip in my tiny story of ephemera and turn it into a challenge to you.
On the edge of my bookshelf was for years a champaign glass, until it fell off into a dozen pieces --as do things in precarious positions. The glass had been engraved with the IBM logo and reminded the date of the opening of some new data center or computing center. I collected it from the flea market.
I picked it up, because to me it represented the lore of emblems, decorations, fountain pens. It is a culture not uncommon in the world of computing, but IBM was particularly good at it, mixing --often macho tainted-- company pride with celebration of technical progress. There was a high culture of walking well suited, of not riding a motercycle when visiting clients, of not spoiling coffee but finishing a job on ephedrine.
Jim, the lore of the coffee mug is all around and, judging from the response, we all have access to this low hanging fruit --I reckon the same would be true of printed T-shirts as ephemera of hacker culture. But few would have access like you have to the high culture of computing, of human struggling with computing --still tacit knowledge but visible to your exquisite ethnographical perception. Help us by collecting the ephemera and anecdotes on the further branches of the tree.
Surprise me with things I would not even have recognized as ephemera of computing culture.
Cheers,
Gerard