Speaking as a former hitchhiker who used it to travel through 39 states, it's actually legal almost everywhere. What is illegal is to stand in the path of travel of a roadway, and in some locations standing on the shoulder is also illegal. But on a sidewalk, onramp, etc, as long as you're not physically in the road, it's almost always ok.

Some exceptions being Utah, Delaware, New Jersey, and maybe another, where you're specifically banned from soliciting rides using signage.

Sadly, the best resource for seeing what the laws are in each state was digihitch.com, which went down in 2014, I believe when the founder passed. Quite sad, they had pamphlets for every state with relevant laws written down -- it came in handy a few times when police stopped me. They were always respectful, but I did have to clarify the laws a few times, since it's clear if read, but not widely understood.

No.

Hitchhiking is technically illegal in 4 states and rarely enforced even there.

http://hitchwiki.org/en/United_States_of_America#Police.2FLa...

I'd love to hear the justification for this.