I took it that the assumption was that Jeff himself knocked down the sign. Dude was doused in beer and cops wanted to close the case and go home... happens everyday. Unless there was somebody forcing the issue or someone breathing to charge they're not wasting resources on running his bac. Sadly everyone was willing to accept he was driving drunk. #jeffdeservedbetter
I just can't buy that.
1. This is a small town. Everyone knows everyone, deaths are big deals, especially deaths of teenagers. This wasn't some bum in a huge city like Los Angeles that skid off the road into a ditch. This was a well liked HS student, star of the local baseball team in the prime of his life leaving a HS party and getting involved in a fatal accident, and injuring someone else in the process. That ain't a "lets just go home" case in a small community. Both the local reporters and the local police would have every reason to dedicate resources to figuring out exactly what happened, at at bare minimum, finding out how drunk the kid was.
2. If the assumption was that Jeff was drunk driving after leaving a big HS party right before school started, this would have cast a lot of scrutiny on the HS students and their parties. Just look at the town's reaction to the suicide with all of their suicide prevention posters and whatnot. There would have been DUI prevention talks, lectures, and probably investigations into these local parties. How drunk are these 15 year olds getting? Who in the local community is providing these sophomores with this much booze?
3. This wasn't just a single person accident, someone else was involved too. Someone that claims he still has nightmares because of the accident. That's a possible lawsuit waiting to happen.
4. It's not a wasted resource. The majority of states require mandatory BAC testing in fatal accidents where drunk driving is suspected. California is one of those states, where this town supposedly is located.
5. And even if none of those points quite resonate - the police don't care, the local reporters don't care, the injuried parties don't care, the school doesn't care, the local governing body doesn't care - what about Jeff's parents? They were equally devastated of their sons sudden death as Hannah's parents. I just don't buy that his parents would not want to know everything about that accident and party, including his BAC level.
One of the things I like most about shows like this is how lived in the world feels. How real the school feels, how real the town feels, how real people in the town feel. For most of the series, they excelled at making everything feel connected and real. But I don't think they did that in this instance, which was irritating because it involved the arc of several characters and came at the emotional climax of the season.
This is a close knit community where everything is in walking and biking distance. That town isn't washing their hands of a DUI related death of a young kid.
I'm one of the people who said she absolutely stupid for being at the party and house of a known rapist a week after u saw him rape your friend. Walk into his house uninvited, strip down to your panties and get in a hot tub. Wtf 
to 
was hilarious.