Gov. Rick Snyder has signed bills banning what is known as so-called synthetic marijuana.   A signing ceremony was held in Lansing yesterday (Tuesday), allowing Michigan to join with some 40 other states in banning substances, some of which are sold under such trade names as Spice and K2, has been available in stores as a mix of dried herbs and spices sprayed with chemicals. Reports say it has been blamed for health problems and violent behavior.  The bills also crack down on products that are referred to as bath salts. The bills also allow the Department of Community Health to declare health dangers when other synthetic drugs might pop up.   While the Governor just signed the bills this week for the state of Michigan, a number of counties and communities already have acted on their own to ban synthetic marijuana