Most plugins that use signs are broken right now because of a change in the way the MCPE client handles sign events. Mojang are actually aware that the lack of an event on sign closure poses a problem for many servers; whether or not they'll add one is unlikely I think, because the new system has advantages... Meanwhile authors don't want to update plugins in case Mojang add an event for sign close . If the next version doesn't have it, I'll start updating those on Poggit-Orphanage to use a different mechanism, and encourage other plugin authors to do the same.
CommandShop adds signs by running a command and then tapping them, this has the advantage of being able to have the text you want on the sign. The difference to normal SignShop plugins is, that with this one you will have to specify a command that gets executed after paying the money which opens the world to unlimited customizability