I have read that only claimed plots will have a sign. You can always do /p info and it gives you the exact same info plus more that a sign would give. Check that you are the actual owner of the plot when doing /p info as something may have happened to your ownership. Not sure how, or what, but check anyway. /p info will only work while standing on a plot. You don't just have to use the command on your plot, but you can go and stand on others too to get info on their plots.
Thanks. What happened is Im the owner, but I got banned (maybe a problem there) And it also says Owner: wwp2005 Denied: wwp2005