I really have always wanted to go hitchhiking across the US.  Do you know anything about hitchhiking?
Sure it is the practice of asking people for a ride in their vehicle to get to a destination.
Do you know when hitchhiking first became popular?
Most likely as soon as motor vehicles became common in the 20th century. Rides are usually free for the hitchhiker.
I wonder how safe hitchhiking is.  Are there any concerns? 
Some people are concerned but there have been few incidents reported. It is common worldwide and usually legal.
Sounds fun.  I think I might try it sometime
If you are in the US or UK you should extend your hand and point your thumb up so motorists know you want a ride.
Thanks for the advice.  I was just going to make a sign
Displaying a written sign is also another method to get a ride. You may want to also look friendly to get a better chance of being picked up.