Hate to start another of these identification threads, but I just can't find much on it... and I swear I've seen it on some member's wrist in one of those WRUW threads (wish I could remember when .. been through several looking for it).
There's nothing to identify it with on the back, and I still haven't managed to get a look at the movement.
I've found this one reference to it: Vintage Watch Price Guide
Search for 688 on that page and you'll see what I found.. found that by searching for "hamilton watch satin dial" in google's image search
Anyway, looking for any additional info someone might have on the model.