It's a billboard that is being used to advertise more towards the locals as a reminder that the event is coming. If you put that billboard in Bangor, ME then I could see your point. Furthermore, you point out how long the URL is... whoa... it's so complex. As long as you can read English, it wouldn't be that difficult to remember. Halloween Horror Nights... yes, much too complicated to remember.
Obviously you can't compare Disney marketing materials, which have existed for many decades, to a random billboard. However, having a billboard that is at least memorable each year would be cool instead of just plain unimaginative material.
And for the record, I'll be lucky to see any advertisements at all for Horror Nights where I am. I think there may have been a commercial or 2 last year which was a 1st. Considering how large the event has become and how popular Halloween has become in general, you'd think they'd market at least a little in the Boston area on tv, but I've yet to really see that happen.