I quite clearly remember that the first time I ever saw the squiggles I wondered why there was water indicated there. However, I'm not sure it would have helped me to see "aquifer"; what that would have done is make me wonder why there was "aquifer" indicated there. So my claim is that it's not the ideogram that's the problem.
The embark screen is very busy as it is; really the only way to make any sense of it as a newbie is to hit up the wiki. There is a page for the embark screen, and you're right, it isn't perfect. If you see a better way to explain it, please fix it. Maybe the ideal is a screenshot with little red boxes calling out the various parts of the screen like there are in major commercial products' manuals, or maybe someone has a better idea?
Well, wouldn't want anyone thinking I wasn't being helpful, so I took a look at it. I don't think a set of red boxes would help much, (the map parts are obvious, the "this button does this" part doesn't need pointing out, and the tabbable part on the right is what holds the most data, which is something that is better described than simply labeled with a box) but I am going through to expand on what the wiki says as much as possible on a single page.
Apparently not in at least a small set of cases, since we've got a thread about it. You'd need to isolate what part the aquifer is represented by, and, given DF's UI, I'd myself wouldn't be sure that the game would actually tell you where the aquifer was if I didn't know better. The fix would be simple with no drawbacks and would make the game less confusing to at least a few people, so I think it's a good decision.
Kohaku - just realize that this type of problem is caused by an unintuitive interface, which is within Toady's power to easily correct and would make for a better game. Having a few of these problems aren't a big deal (and it happens in quite a few games), but DF's major problem is in having so many of these unintuitive bits in a tight cluster. At this point, the UI's confusion has achieved a critical mass that keeps lots of players away.
You can claim it's just laziness on the parts of the players, but the more time people spend struggling with the interface, the less fun the game holds for them (and the more things they need to look up, the more likely they to hit their threshold of annoyance and to just completely drop the game.)
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EDIT: Fixing these minor problems will lead to less threads posted about them too, a prospect which will no doubt make you happier, Kohaku.
The problem with that is what I've been posting before: They wouldn't stop people from finding new ways to try to misinterpret something. It's like the old Tech Support horror stories: A guy calls up IT, and says "My computer keeps saying it can't find the printer! I'm even holding it up right in front of the moniter, and it still says it can't find it!"
Which brings me back to the point: There may be many things about DF that are fairly unintuitive and even downright obtuse, and sure, I'd like plenty of UI changes to take place, but
this isn't one of them. Even the original poster has said he recognized it as water when he actually looked at it, the game is internally consistant about the blue double tildes being water, and the game comes out and warns you that it is an aquifer, so that there is no confusion, other than, as numerobis said, possibly the confusion of what an aquifer actually means. And if you don't know what it means, there's nothing you could put on the interface, other than a full mouse-based hyperlinked in-game encyclopedia (good luck begging Toady for THAT!), that will be more useful to you than going on the wiki.
This really is as simple as it gets. If you get the internally consistant symbol for water, and cannot figure out it means water, followed by a pop-up that says in clear language that there is an aquifer there without figuring out that it means an aquifer is there... well, maybe you SHOULD just play a different game.
As an example:
I don't know how much faith you place in Valve's design team, but their game environments are carefully picked through to make sure they don't cause confusion in their players to a rather obscene extent (you can see this if you look at the developer commentaries in Portal.) I myself would call it a bit excessive, but I still do think it's a huge reason that their games are so dominant - by making it as easy as possible to know what the game's environment and UI allow you to do, you can put the focus on enjoying more important things. It disrupts the flow of the game to have to look up stuff in a wiki or in a manual, and screws with another kind of flow that's really useful to games too. Any game - *especially* Dwarf Fortress, because of its complexity - should minimize interruptions because it disrupts players' enjoyment.
I wouldn't really know, as I am not much of a FPS player.
I also do not feel much "flow" at all in DF, as the game is generally played with 95% forethought, reading data from menus, and planning, 4% punching in commands, and 1% just watching the little ants run through the ant farm.