able to place signs on Minecarts of all varients

Im currently designing some auto furnacing that require hopper minecarts. got kind of mixed up with which minecart had to be only transferring coal and the other one to be transferring my raw material. thought it would a good idea to place signs indicating what should be going in each minecart. It doesn't even have to be for that stuff. you can also indicate which minecart is whose on a server