I bonds in particular are closer to a CD and are not transferable. If you have access to credit, you could borrow and pay it back once your I bond matures is cashable. Other Treasury notes can be sold, though if rates go up you may get back less than your principal, particularly on the longer duration notes.

Treasury rules? No redeeming for 1 year, and redeeming before 5 years means you lose the last 3 months of interest. You can gift them to other people though.

They're issued to you, and have your name on them.

Nothing, you can buy and sell them in the secondary market.