The problem with El Salvador is that it's a better lock up 9 innocent people than let one guilty person go free type of problem now. And it is guilt by how you look and some association.
It's great if you're a tourist with limited Spanish ability and are tired of Costa Rica. Very shitty if you have any family members that get thrown in jail forever with out due process based on how the government felt they looked.
It's also apparently great if you live in El Salvador. His approval rating is > 90% and has been flirting with getting mighty close to 100% +/- statistical noise. Gang tattoos are not random - they are intentionally designed and chosen to indicate your unambiguous affiliation with a specific gang in order to prove loyalty and acceptance. In many cases they can also go much further indicating rank, crimes committed, and more.
They are also often done in very visible places, including the face and hands. Here [1] for instance are various individuals with MS-13 (which was a group initially started by Salvadoran migrants in LA) tattoos. You're not going to make a mistake there, and the gang itself would have also also taken care of imposters.
The groups expressing concern about the gang members tend to be Western human rights organizations in different countries. The president of El Salvador has offered to allow the countries of these groups to take in as many of the prisoners as they would like, if they'd like to more personally look after and ensure their rights. His offers have not been accepted.
It's great if you're a tourist with limited Spanish ability and are tired of Costa Rica. Very shitty if you have any family members that get thrown in jail forever with out due process based on how the government felt they looked.