You were trying to open the chests by clicking on the sign, maybe try clicking on the chest? Otherwise I don't know what the issue could be.
Yep, sometimes you need to open the chest by actually clicking on the chest instead of the sign.... Did you change your name? Your not suppose to be able to buy your own items.... So either that is someone with a super close to exact same name or you changed your name and forgot to remove the signs before you do...
Closing this for inactivity. If you are still experiencing this specific issue and wish for this thread to be reopened, feel free to message a staff member to reopen this for you.