To my view, this is a pretty straightforward fix. If the existing signage isn't working effectively, re-work it. The signage orientation and presentation should give hikers from all 3 directions a clear indication of where the two forks lead. That's just simply a no-brainer, right? If they're not oriented in an eye-catching manner - especially for novice hikers coming up from the Portal or down from the summit - it sounds like a pretty easy fix: re-work the existing signage with special attention to keeping first-timers aware of which direction is which.
Granted, that won't necessarily stop some disoriented or distracted hikers from going down instead of up, or right instead of left - stuff happens - but at least it might help prevent a case or two of wrong way-itis that results in a SAR call. A single hour of a SAR has to more expensive and time-consuming than replacing a less-than-effective signpost. It's already there - no need to add another and another - just re-configure it to produce a better result. Directional signage should be clear and work, whether it's on a 14-lane freeway or in the wilderness. Otherwise, what's the point?
Personally, since everyone has to pick up their permit at the Inter-Agency Center prior to hitting the trail, I think that's where the other "best" solution may lie - education. Something, anything, that cries, "Do this and you'll die!". Okay, maybe not that dramatic, but you get the idea. A WZ hiker has to initial that a Ranger has discussed regulations, wag bags, food storage, etc with them, but no key safety points based on recurring problems. This sounds like a recurring problem over the years, so I'm just a bit amazed it's still status quo. I would imagine a half-baked, ambulance-chasing, personal injury attorney would have a field day in court with this set of circumstances if it ever came to it.
I agree wholeheartedly that novice, unprepared hikers shouldn't necessarily have their hand held when venturing into the wilderness. It's not a game and Mommy's not with you (well, there's SPOT, but that's a completely different topic). Unfortunately, many of these folks seem to be drawn to and congregate at Whitney, and that's just a fact. It's a magnet for everyone because of what it is and what it represents. Given the unique nature of the mountain, and the broader spectrum of it's hiking audience, I think a little extra diligence on Sequoia or INF's part is necessary to help prevent what appears to be an often-repeated mistake that can turn deadly.
