Hardly. We all know trump will never actually see a day behind bars. This sign is a comment on how he should be in prison. It's also referring to the karma (not justice) of him getting raped due to all his raping. It also is more appropriate as the GOP aims to put more people in crappy private prisons, without even attempting to solve the prison rape problem. And their public fear of homosexuality played into it as well.
It's not meant to be taken literally and it's a not an endorsement of actual prison rape. It is a message of protest against a president who is a traitor and deserves a bullet in the head. It's edgy to get attention to the cause against trump. Those of us who don't want a fascist U.S. shouldn't fight over minor things like this. Such purity tests will divide and destroy us.