Now there's a logo you don't see often, and as far as I could tell, this is the one and only time in Thor's run that it was used as the main title on the front of the book. It pops up on internal pages as early as Journey Into Mystery #87:
And it made a later rare cover appearance on Journey Into Mystery #99:
I'm not certain who created the logo for JIM #87 (possibly letterer Artie Simek?) and I suppose despite its tryout, Stan may have thought it didn't convey the grandeur and glory of Marvel's golden-tressed Asgardian powerhouse. I can't quite put my finger on it, but I'd say at first glance it doesn't look like a Marvel comics logo. Even if you weren't familiar with the usual Thor logo, this looks much more like, say, a Charlton logo. That woulda been a heartburn to Stan.
As far as I can tell, it isn't seen on Thor covers aside from King-Size Special #4 and JIM #99. It's kinda a shame: it's a nice, dramatic, dynamic logo that leaps right out at you from the spinner rack at Pop's Chok'lit Shop, but it's a little more cartoony (thanks to the exclamation point) than the usual jagged-rock Thor logo that was the standard (until the early Walt Simonson issues). Whatever was the thinking behind using this logo on King-Sized Special #4, we'll never know it. But it makes a nifty thing of wonder to gaze at and ponder, and when you can do that with a comic book logo, you know you're a true fan, because it's not only the stories and the characters that make comics fun--it's the history and mystery behind them.