It’s a design for a t-shirt/coffee mug. I don’t get it. Is it some computer based thing that I don’t know or is the design supposed to look like something (a schooner?) and I don’t see it.
For some reason, the first thing I thought of when I saw it was “Pac Man”. 
Go here: http://en.wikipedia.org/wiki/Nethack
Learn.
nethack was a dungeon crawling game from way back in the day, it had minimal graphics, using letters to represent monsters, greater then signs to represent staircases, other ascii symbols to represent other things. That design is an example of a room one might find in nethack
Heh. And now that I didn’t get outgunned by some other Doper 
— As Taber said the shirt is a reference to Nethack (a Rogue clone). It’s like having a shirt with King Graham on it, or the Pong Paddles. It’s an homage.
Nethack is world famous in Poland for being the most popular of the Rogue-type dungeon-exploration games. These games were characterized by their low-key graphics (usually just using standard text characters) and for sucking up billions of nerd-hours across the globe.
The wiki link provides much more data. But I would recommend you download it and give it a look yourself (it’s free).
You can also do a search for nethack on the Dope and read various entertaining threads about it.
- Peter Wiggen
So I should stop trying to find a schooner?
Yes. Look for a sailboat instead. 
And I don’t think it’s meant to be funny… unless I am missing something too.
I remember playing a predecessor to this game called “Mansion” back in the late 70s. OMFG I’m old.
Well, it’s a little funny just in the sense that it would confuse people who don’t know what the heck it’s supposed to be, and make immediate sense to anyone who’s ever played a rogue game.
Let’s see how many parts of that particular picture I can identify. There’s a rectangular room with two dark tunnel passages leading out of it, and one staircase… is that a down staircase? Our hero is pretty much in the middle of the room, with a pack of nasties - giant rats maybe? - emerging from one of the tunnels. There’s some sort of gold or treasure lying nearby, and… possibly a potion bottle sitting next to the north wall?
It’s an up staircase.
Square room; in fact, if the adventurer has been plenty unlucky and his pet has died or been poly’d into a rat, this could be the very first room. There’s a potion off to the upper left and a pile of money off to the upper right, two doorways leading out into a hallway, and three rats coming in.
Considering that the hallway on the lower right is partly explored, I would suggest that Our Hero is a somewhat lower-level adventurer who does most of his fighting from a distance. A wizard would probably let a spell loose from the doorway so that he could catch multiple critters in one blast, so my initial assessment is that we are looking at a low-level Tourist who has nothing but a large quantity of magic darts to throw at his opponents.
Yeah, I play this game WAY too much. You might ask yourself (you might even ask me) why I’d play Nethack when there’s games like World of Warcraft or even Diablo or Baldur’s Gate, several levels of visual complexity above this one.
To answer that… well, I’d have to give you a very long post. 
We had a game on our Commodore 64 that was similar but not quite the same. You started with a blank screen and as you moved the cursor around you found the limits of the room and things like Wyverns (which were Xs) and Dragons (which were Clubs) and Gold (which was a G) and the point was to expose every square in the dungeon.
I’ve always wondered what that game was. I wiled away many ours in the early 80s on it. I think we had it on cassette!
Heh
Or maybe it IS a joke. Let’s see, a room, an @, a !.. so three rats walk into a bar…
OMG, that fits too!
Was? Was??? It is an adventure game. You can play using ascii or graphics.
Nethack is the bestest game EVAR. “IS”! Present tense. Take that, Halo 2.
(I have this very shirt, actually)