So regarding that CW Las Vegas promo. The locker is definately Jughead’s. At the beginning of episode 2 there is a flashback of Jughead in front of his locker watching Jason walking by; the angle of the two scenes matches as well as the fact that the locker is second (or third) from the right. Also, in the same episode we see Betty at her locker talking to Veronica and its location is further down the corridor and to the opposite side of the locker in the CW clip. So the threatening/offensive banners are hanging on Jughead’s locker. There’s the voodoo doll of Betty there too though. So my thoughts are these: 

1. whoever did this wants to threaten both of them because a.they are simply a couple b.they are investigating Jason’s murder together so they are both responsible for revealing the killer c.we learn something in the next episodes that ties their families together and involves them to the murder.

2. (this thought is painful) whoever did this is actually threatening/ridiculing Jughead and/or his father and Betty’s doll next to it, hanging actually, is a sick joke about the fact that Jughead is a phycopath and sooner or later Betty herself is gonna end up like Jason Blossom because of him. That’s why Jughead looks petrified and Betty rushes to take everything down, looking hurt (?). 

I don’t know, the wheels in my mind are turning viciously right now and taking me to dark imaginative places :p